diff --git a/src/main/java/mops/gruppen2/controller/Gruppen2Controller.java b/src/main/java/mops/gruppen2/controller/Gruppen2Controller.java
index 842870d..217231b 100644
--- a/src/main/java/mops/gruppen2/controller/Gruppen2Controller.java
+++ b/src/main/java/mops/gruppen2/controller/Gruppen2Controller.java
@@ -2,19 +2,16 @@ package mops.gruppen2.controller;
 
 import mops.gruppen2.config.Gruppen2Config;
 import mops.gruppen2.domain.Exceptions.EventException;
+import mops.gruppen2.domain.Exceptions.GroupNotFoundException;
 import mops.gruppen2.domain.Group;
 import mops.gruppen2.domain.User;
-import mops.gruppen2.domain.Visibility;
-import mops.gruppen2.domain.event.CreateGroupEvent;
 import mops.gruppen2.security.Account;
 import mops.gruppen2.service.*;
 import org.keycloak.adapters.springsecurity.token.KeycloakAuthenticationToken;
 import org.springframework.beans.factory.annotation.Autowired;
-import org.springframework.http.HttpStatus;
 import org.springframework.stereotype.Controller;
 import org.springframework.ui.Model;
 import org.springframework.web.bind.annotation.*;
-import org.springframework.web.client.RestTemplate;
 import org.springframework.web.context.annotation.SessionScope;
 import org.springframework.web.multipart.MultipartFile;
 import org.springframework.web.server.ResponseStatusException;
@@ -125,7 +122,7 @@ public class Gruppen2Controller {
 
     @RolesAllowed({"ROLE_orga", "ROLE_studentin", "ROLE_actuator"})
     @GetMapping("/details")
-    public String showGroupDetails(KeycloakAuthenticationToken token, Model model, @RequestParam(value = "id") Long id) throws EventException, ResponseStatusException {
+    public String showGroupDetails(KeycloakAuthenticationToken token, Model model, @RequestParam(value = "id") Long id) throws ResponseStatusException, EventException {
         model.addAttribute("account", keyCloakService.createAccountFromPrincipal(token));
         Group group = userService.getGroupById(id);
         Account account = keyCloakService.createAccountFromPrincipal(token);
@@ -135,7 +132,7 @@ public class Gruppen2Controller {
             model.addAttribute("role", group.getRoles().get(user.getUser_id()));
             return "detailsMember";
         }
-        throw new ResponseStatusException(HttpStatus.NOT_FOUND, "Group not found");
+        throw new GroupNotFoundException();
     }
 
     @RolesAllowed({"ROLE_orga", "ROLE_studentin", "ROLE_actuator"})
@@ -156,7 +153,7 @@ public class Gruppen2Controller {
             model.addAttribute("group", group);
             return "detailsNoMember";
         }
-        throw new ResponseStatusException(HttpStatus.NOT_FOUND, "Group not found");
+        throw new GroupNotFoundException();
     }
 
     @RolesAllowed({"ROLE_orga", "ROLE_studentin", "ROLE_actuator"})
@@ -168,10 +165,10 @@ public class Gruppen2Controller {
             model.addAttribute("group", group);
             return "redirect:/gruppen2/detailsSearch?id=" + group.getId();
         }
-        throw new ResponseStatusException(HttpStatus.NOT_FOUND, "Group not found");
+        throw new GroupNotFoundException();
     }
 
-    @RolesAllowed({"ROLE_orga", "ROLE_studentin", "ROLE_actuator"})
+    @RolesAllowed({"ROLE_orga", "ROLE_studentin", "ROLE_actuator)"})
     @PostMapping("/leaveGroup")
     public String pLeaveGroup(KeycloakAuthenticationToken token, @RequestParam(value = "group_id") Long id) {
         Account account = keyCloakService.createAccountFromPrincipal(token);
@@ -181,6 +178,6 @@ public class Gruppen2Controller {
 
     @GetMapping("*")
     public String defaultLink() {
-        return "errorRenameLater";
+        return "error";
     }
 }
diff --git a/src/main/java/mops/gruppen2/domain/Exceptions/EventException.java b/src/main/java/mops/gruppen2/domain/Exceptions/EventException.java
index 20bb176..e562f51 100644
--- a/src/main/java/mops/gruppen2/domain/Exceptions/EventException.java
+++ b/src/main/java/mops/gruppen2/domain/Exceptions/EventException.java
@@ -1,10 +1,13 @@
 package mops.gruppen2.domain.Exceptions;
 
-public class EventException extends Exception {
+import org.springframework.http.HttpStatus;
+import org.springframework.web.server.ResponseStatusException;
+
+public class EventException extends ResponseStatusException {
     private String msg;
 
-    public EventException(String msg) {
-        this.msg = msg;
+    public EventException(String msg, HttpStatus status) {
+        super(status, msg);
     }
 
     @Override
diff --git a/src/main/java/mops/gruppen2/domain/Exceptions/GroupIdMismatchException.java b/src/main/java/mops/gruppen2/domain/Exceptions/GroupIdMismatchException.java
new file mode 100644
index 0000000..3d98e69
--- /dev/null
+++ b/src/main/java/mops/gruppen2/domain/Exceptions/GroupIdMismatchException.java
@@ -0,0 +1,13 @@
+package mops.gruppen2.domain.Exceptions;
+
+import org.springframework.http.HttpStatus;
+
+public class GroupIdMismatchException extends EventException {
+    public GroupIdMismatchException(String msg) {
+        super("Falsche Gruppe für Event." + "    (" + msg + ")", HttpStatus.INTERNAL_SERVER_ERROR);
+    }
+
+    public GroupIdMismatchException() {
+        super("", HttpStatus.INTERNAL_SERVER_ERROR);
+    }
+}
diff --git a/src/main/java/mops/gruppen2/domain/Exceptions/GroupNotFoundException.java b/src/main/java/mops/gruppen2/domain/Exceptions/GroupNotFoundException.java
new file mode 100644
index 0000000..ca45554
--- /dev/null
+++ b/src/main/java/mops/gruppen2/domain/Exceptions/GroupNotFoundException.java
@@ -0,0 +1,13 @@
+package mops.gruppen2.domain.Exceptions;
+
+import org.springframework.http.HttpStatus;
+
+public class GroupNotFoundException extends EventException {
+    public GroupNotFoundException(String msg) {
+        super(msg, HttpStatus.NOT_FOUND);
+    }
+
+    public GroupNotFoundException() {
+        super("Gruppe nicht gefunden.", HttpStatus.NOT_FOUND);
+    }
+}
diff --git a/src/main/java/mops/gruppen2/domain/Exceptions/UserAlreadyExistsException.java b/src/main/java/mops/gruppen2/domain/Exceptions/UserAlreadyExistsException.java
index 8896356..07b593e 100644
--- a/src/main/java/mops/gruppen2/domain/Exceptions/UserAlreadyExistsException.java
+++ b/src/main/java/mops/gruppen2/domain/Exceptions/UserAlreadyExistsException.java
@@ -1,7 +1,13 @@
 package mops.gruppen2.domain.Exceptions;
 
+import org.springframework.http.HttpStatus;
+
 public class UserAlreadyExistsException extends EventException {
-   public UserAlreadyExistsException(String msg){
-       super(msg);
+    public UserAlreadyExistsException(String msg) {
+        super(msg, HttpStatus.INTERNAL_SERVER_ERROR);
+    }
+
+    public UserAlreadyExistsException() {
+        super("Der User existiert bereits.", HttpStatus.INTERNAL_SERVER_ERROR);
     }
 }
diff --git a/src/main/java/mops/gruppen2/domain/Exceptions/UserNotFoundException.java b/src/main/java/mops/gruppen2/domain/Exceptions/UserNotFoundException.java
index f7e0080..fd10bb9 100644
--- a/src/main/java/mops/gruppen2/domain/Exceptions/UserNotFoundException.java
+++ b/src/main/java/mops/gruppen2/domain/Exceptions/UserNotFoundException.java
@@ -1,7 +1,13 @@
 package mops.gruppen2.domain.Exceptions;
 
-public class UserNotFoundException extends EventException{
-    public  UserNotFoundException(String msg){
-        super(msg);
+import org.springframework.http.HttpStatus;
+
+public class UserNotFoundException extends EventException {
+    public UserNotFoundException(String msg) {
+        super(msg, HttpStatus.NOT_FOUND);
+    }
+
+    public UserNotFoundException() {
+        super("Der User wurde nicht gefunden.", HttpStatus.NOT_FOUND);
     }
 }
diff --git a/src/main/java/mops/gruppen2/domain/ProductSwaggerExample.java b/src/main/java/mops/gruppen2/domain/ProductSwaggerExample.java
deleted file mode 100644
index 14f50dd..0000000
--- a/src/main/java/mops/gruppen2/domain/ProductSwaggerExample.java
+++ /dev/null
@@ -1,12 +0,0 @@
-package mops.gruppen2.domain;
-
-import lombok.Value;
-
-// @ApiModelProperty
-@Value
-public class ProductSwaggerExample {
-
-    // @ApiModelProperty
-    String name;
-    String description;
-}
diff --git a/src/main/java/mops/gruppen2/domain/event/AddUserEvent.java b/src/main/java/mops/gruppen2/domain/event/AddUserEvent.java
index a97845c..9f36bce 100644
--- a/src/main/java/mops/gruppen2/domain/event/AddUserEvent.java
+++ b/src/main/java/mops/gruppen2/domain/event/AddUserEvent.java
@@ -27,11 +27,12 @@ public class AddUserEvent extends Event {
         this.email = email;
     }
 
-    public void apply(Group group) throws EventException{
+    @Override
+    public void applyEvent(Group group) throws EventException {
         User user = new User(this.user_id, this.givenname, this.familyname, this.email);
 
-        if (group.getMembers().contains(user)){
-            throw new UserAlreadyExistsException("Der User existiert bereits");
+        if (group.getMembers().contains(user)) {
+            throw new UserAlreadyExistsException();
         }
 
         group.getMembers().add(user);
diff --git a/src/main/java/mops/gruppen2/domain/event/CreateGroupEvent.java b/src/main/java/mops/gruppen2/domain/event/CreateGroupEvent.java
index f5f49b1..878f2b6 100644
--- a/src/main/java/mops/gruppen2/domain/event/CreateGroupEvent.java
+++ b/src/main/java/mops/gruppen2/domain/event/CreateGroupEvent.java
@@ -15,8 +15,6 @@ public class CreateGroupEvent extends Event {
     private Long groupParent;
     private GroupType groupType;
 
-
-
     public CreateGroupEvent(Long group_id, String user_id, Long parent, GroupType type, Visibility visibility) {
         super(group_id, user_id);
         this.groupParent = parent;
@@ -24,7 +22,8 @@ public class CreateGroupEvent extends Event {
         this.groupVisibility = visibility;
     }
 
-    public void apply(Group group) {
+    @Override
+    public void applyEvent(Group group) {
         group.setId(this.group_id);
         group.setParent(this.groupParent);
         group.setType(this.groupType);
diff --git a/src/main/java/mops/gruppen2/domain/event/DeleteGroupEvent.java b/src/main/java/mops/gruppen2/domain/event/DeleteGroupEvent.java
index 4b8a6e3..0640d8d 100644
--- a/src/main/java/mops/gruppen2/domain/event/DeleteGroupEvent.java
+++ b/src/main/java/mops/gruppen2/domain/event/DeleteGroupEvent.java
@@ -13,7 +13,7 @@ public class DeleteGroupEvent extends Event {
     }
 
     @Override
-    public void apply(Group group) {
+    public void applyEvent(Group group) {
         group.getRoles().clear();
         group.getMembers().clear();
         group.setTitle(null);
diff --git a/src/main/java/mops/gruppen2/domain/event/DeleteUserEvent.java b/src/main/java/mops/gruppen2/domain/event/DeleteUserEvent.java
index 1afab84..00c81ca 100644
--- a/src/main/java/mops/gruppen2/domain/event/DeleteUserEvent.java
+++ b/src/main/java/mops/gruppen2/domain/event/DeleteUserEvent.java
@@ -1,11 +1,11 @@
 package mops.gruppen2.domain.event;
 
-import lombok.*;
+import lombok.Getter;
+import lombok.NoArgsConstructor;
 import mops.gruppen2.domain.Exceptions.EventException;
 import mops.gruppen2.domain.Exceptions.UserNotFoundException;
 import mops.gruppen2.domain.Group;
 import mops.gruppen2.domain.User;
-import mops.gruppen2.domain.Group;
 
 /**
  * Entfernt ein einzelnes Mitglied einer Gruppe.
@@ -17,7 +17,8 @@ public class DeleteUserEvent extends Event {
         super(group_id, user_id);
     }
 
-    public void apply(Group group) throws EventException {
+    @Override
+    public void applyEvent(Group group) throws EventException {
         for (User user : group.getMembers()) {
             if (user.getUser_id().equals(this.user_id)) {
                 group.getMembers().remove(user);
diff --git a/src/main/java/mops/gruppen2/domain/event/Event.java b/src/main/java/mops/gruppen2/domain/event/Event.java
index 17a00f9..cac4b9d 100644
--- a/src/main/java/mops/gruppen2/domain/event/Event.java
+++ b/src/main/java/mops/gruppen2/domain/event/Event.java
@@ -31,7 +31,22 @@ public class Event {
     Long group_id;
     String user_id;
 
-
     public void apply(Group group) throws EventException {
+        checkGroupIdMatch(group.getId());
+        applyEvent(group);
+    }
+
+    protected void applyEvent(Group group) throws EventException {
+
+    }
+
+    private void checkGroupIdMatch(Long group_id) {
+        if (this.group_id.equals(group_id)) {
+            return;
+        }
+
+        //throw new GroupIdMismatchException(this.getClass().toString());
+        System.out.println(group_id);
+        System.out.println(this.group_id);
     }
 }
diff --git a/src/main/java/mops/gruppen2/domain/event/UpdateGroupDescriptionEvent.java b/src/main/java/mops/gruppen2/domain/event/UpdateGroupDescriptionEvent.java
index 83d4e88..8024365 100644
--- a/src/main/java/mops/gruppen2/domain/event/UpdateGroupDescriptionEvent.java
+++ b/src/main/java/mops/gruppen2/domain/event/UpdateGroupDescriptionEvent.java
@@ -19,7 +19,8 @@ public class UpdateGroupDescriptionEvent extends Event {
         this.newGroupDescription = newGroupDescription;
     }
 
-    public void apply(Group group) {
+    @Override
+    public void applyEvent(Group group) {
         group.setDescription(this.newGroupDescription);
     }
 }
diff --git a/src/main/java/mops/gruppen2/domain/event/UpdateGroupTitleEvent.java b/src/main/java/mops/gruppen2/domain/event/UpdateGroupTitleEvent.java
index dffb13d..7f2f1d1 100644
--- a/src/main/java/mops/gruppen2/domain/event/UpdateGroupTitleEvent.java
+++ b/src/main/java/mops/gruppen2/domain/event/UpdateGroupTitleEvent.java
@@ -19,7 +19,8 @@ public class UpdateGroupTitleEvent extends Event {
         this.newGroupTitle = newGroupTitle;
     }
 
-    public void apply(Group group) {
+    @Override
+    public void applyEvent(Group group) {
         group.setTitle(this.newGroupTitle);
     }
 
diff --git a/src/main/java/mops/gruppen2/domain/event/UpdateRoleEvent.java b/src/main/java/mops/gruppen2/domain/event/UpdateRoleEvent.java
index eeea3d9..64b488e 100644
--- a/src/main/java/mops/gruppen2/domain/event/UpdateRoleEvent.java
+++ b/src/main/java/mops/gruppen2/domain/event/UpdateRoleEvent.java
@@ -1,13 +1,11 @@
 package mops.gruppen2.domain.event;
 
-import lombok.*;
-import mops.gruppen2.domain.Exceptions.EventException;
+import lombok.AllArgsConstructor;
+import lombok.Getter;
+import lombok.NoArgsConstructor;
 import mops.gruppen2.domain.Exceptions.UserNotFoundException;
 import mops.gruppen2.domain.Group;
 import mops.gruppen2.domain.Role;
-import mops.gruppen2.domain.User;
-
-import java.util.Optional;
 
 /**
  * Aktualisiert die Gruppenrolle eines Teilnehmers.
@@ -18,15 +16,16 @@ import java.util.Optional;
 public class UpdateRoleEvent extends Event {
 
     Role newRole;
-  
+
     public UpdateRoleEvent(Long group_id, String user_id, Role newRole) {
         super(group_id, user_id);
         this.newRole = newRole;
     }
 
-    public void apply(Group group) throws UserNotFoundException{
-        if (!group.getRoles().containsKey(user_id)){
-            throw new UserNotFoundException("Der User wurde nicht gefunden");
+    @Override
+    public void applyEvent(Group group) throws UserNotFoundException {
+        if (!group.getRoles().containsKey(user_id)) {
+            throw new UserNotFoundException();
         }
         group.getRoles().put(this.user_id, this.newRole);
     }
diff --git a/src/main/java/mops/gruppen2/security/SecurityConfig.java b/src/main/java/mops/gruppen2/security/SecurityConfig.java
index 8816b24..df96dd7 100644
--- a/src/main/java/mops/gruppen2/security/SecurityConfig.java
+++ b/src/main/java/mops/gruppen2/security/SecurityConfig.java
@@ -6,11 +6,7 @@ import org.keycloak.adapters.springsecurity.authentication.KeycloakAuthenticatio
 import org.keycloak.adapters.springsecurity.config.KeycloakWebSecurityConfigurerAdapter;
 import org.keycloak.representations.AccessToken;
 import org.springframework.beans.factory.annotation.Autowired;
-import org.springframework.context.annotation.Bean;
-import org.springframework.context.annotation.ComponentScan;
-import org.springframework.context.annotation.Configuration;
-import org.springframework.context.annotation.Scope;
-import org.springframework.context.annotation.ScopedProxyMode;
+import org.springframework.context.annotation.*;
 import org.springframework.security.config.annotation.authentication.builders.AuthenticationManagerBuilder;
 import org.springframework.security.config.annotation.method.configuration.EnableGlobalMethodSecurity;
 import org.springframework.security.config.annotation.method.configuration.GlobalMethodSecurityConfiguration;
diff --git a/src/main/java/mops/gruppen2/service/UserService.java b/src/main/java/mops/gruppen2/service/UserService.java
index 74a9ca4..681b3c6 100644
--- a/src/main/java/mops/gruppen2/service/UserService.java
+++ b/src/main/java/mops/gruppen2/service/UserService.java
@@ -1,6 +1,7 @@
 package mops.gruppen2.service;
 
 import mops.gruppen2.domain.Exceptions.EventException;
+import mops.gruppen2.domain.Exceptions.GroupNotFoundException;
 import mops.gruppen2.domain.Group;
 import mops.gruppen2.domain.User;
 import mops.gruppen2.domain.event.Event;
@@ -39,7 +40,12 @@ public class UserService {
     public Group getGroupById(Long group_id) throws EventException {
         List<Long> group_ids = new ArrayList<>();
         group_ids.add(group_id);
-        List<Event> events = groupService.getGroupEvents(group_ids);
-        return groupService.projectEventList(events).get(0);
+
+        try {
+            List<Event> events = groupService.getGroupEvents(group_ids);
+            return groupService.projectEventList(events).get(0);
+        } catch (IndexOutOfBoundsException e) {
+            throw new GroupNotFoundException("Gruppe nicht gefunden");
+        }
     }
 }
diff --git a/src/main/resources/application-dev.properties b/src/main/resources/application-dev.properties
index ee53a97..bc79d39 100644
--- a/src/main/resources/application-dev.properties
+++ b/src/main/resources/application-dev.properties
@@ -18,4 +18,5 @@ keycloak.verify-token-audience=true
 keycloak.use-resource-role-mappings=true
 
 keycloak.autodetect-bearer-only=true
-keycloak.confidential-port= 443
+keycloak.confidential-port=443
+server.error.include-stacktrace=always
diff --git a/src/main/resources/templates/error.html b/src/main/resources/templates/error.html
new file mode 100644
index 0000000..5ea8655
--- /dev/null
+++ b/src/main/resources/templates/error.html
@@ -0,0 +1,34 @@
+<!DOCTYPE html>
+
+<html lang="en" xmlns:th="http://www.thymeleaf.org">
+<head>
+    <meta charset="utf-8">
+    <meta content="width=device-width, initial-scale=1, shrink-to-fit=no" name="viewport">
+    <link crossorigin="anonymous" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0/css/bootstrap.min.css"
+          integrity="sha384-Gn5384xqQ1aoWXA+058RXPxPg6fy4IWvTNh0E263XmFcJlSAwiGgFAW/dAiS6JXm" rel="stylesheet">
+    <meta charset="UTF-8">
+    <title>Seite nicht gefunden</title>
+</head>
+<body>
+<div class="mx-auto" style="vertical-align: center; horiz-align: center; top: 50%; left: 50%;">
+    <div class="jumbotron" style="background: aliceblue">
+        <div class="container">
+            <h1 class="display-3">UPSI</h1>
+            <p class="lead">Da ist wohl etwas schiefgelaufen :(</p><br>
+        </div>
+    </div>
+    <div class="container">
+        <div class="card mb-4 shadow-sm">
+            <div class="card-header">
+                <h4 class="my-0 font-weight-normal" th:text="${status} + ': ' + ${error}"></h4>
+            </div>
+            <div class="card-body">
+                <p th:text="${message}"></p>
+            </div>
+        </div>
+        <p><a class="btn btn-primary btn-lg" href="#" onclick="window.history.back(-1);return false;" role="button">Zurück</a>
+        </p>
+    </div>
+</div>
+</body>
+</html>
diff --git a/src/main/resources/templates/errorRenameLater.html b/src/main/resources/templates/errorRenameLater.html
deleted file mode 100644
index 01fbadc..0000000
--- a/src/main/resources/templates/errorRenameLater.html
+++ /dev/null
@@ -1,26 +0,0 @@
-<!DOCTYPE html>
-
-<html lang="en" xmlns:th="http://www.thymeleaf.org">
-<head>
-    <meta charset="utf-8">
-    <meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">
-    <link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0/css/bootstrap.min.css" integrity="sha384-Gn5384xqQ1aoWXA+058RXPxPg6fy4IWvTNh0E263XmFcJlSAwiGgFAW/dAiS6JXm" crossorigin="anonymous">
-    <meta charset="UTF-8">
-    <title>Error</title>
-</head>
-<body>
-<div class="mx-auto" style="vertical-align: center; horiz-align: center; top: 50%; left: 50%; margin-top: 200px">
-    <div class="text-center" style="background: aliceblue; align-items: center; margin: auto; width: 1000px; vertical-align: center; padding: 50px; display: block">
-        <h1 style="text-align: center">Da ist etwas schiefgelaufen!</h1>
-        <h2 style="text-align: center">Die Seite, nach der du suchst, scheint nicht zu existieren.</h2>
-        <br>
-        <div>
-            <button type="button" class="btn btn-primary" style="margin: auto">
-                <a style="color: white" href="#" onclick="javascript:window.history.back(-1);return false;">Zurück zur letzten Seite</a>
-            </button>
-        </div>
-        <br>
-    </div>
-</div>
-</body>
-</html>
\ No newline at end of file