diff --git a/package.json b/package.json
index 5587b6c..fb4a2c1 100644
--- a/package.json
+++ b/package.json
@@ -61,11 +61,13 @@
     "react-datepicker": "^8.4.0",
     "react-day-picker": "^9.7.0",
     "react-dom": "^19.0.0",
+    "react-error-boundary": "^6.0.0",
     "react-hook-form": "^7.56.4",
     "sonner": "^2.0.5",
     "swagger-ui-react": "^5.24.1",
     "tailwind-merge": "^3.2.0",
-    "zod": "^3.25.60"
+    "zod": "^3.25.60",
+    "zod-validation-error": "^3.5.2"
   },
   "devDependencies": {
     "@eslint/eslintrc": "3.3.1",
diff --git a/src/app/api/user/[user]/calendar/validation.ts b/src/app/api/user/[user]/calendar/validation.ts
index 996307f..1572793 100644
--- a/src/app/api/user/[user]/calendar/validation.ts
+++ b/src/app/api/user/[user]/calendar/validation.ts
@@ -19,18 +19,22 @@ export const BlockedSlotSchema = zod
     description: 'Blocked time slot in the user calendar',
   });
 
-export const OwnedBlockedSlotSchema = BlockedSlotSchema.extend({
-  id: zod.string(),
-  reason: zod.string().nullish(),
-  is_recurring: zod.boolean().default(false),
-  recurrence_end_date: zod.date().nullish(),
-  rrule: zod.string().nullish(),
-  created_at: zod.date().nullish(),
-  updated_at: zod.date().nullish(),
-  type: zod.literal('blocked_owned'),
-}).openapi('OwnedBlockedSlotSchema', {
-  description: 'Blocked slot owned by the user',
-});
+export const OwnedBlockedSlotSchema = zod
+  .object({
+    start_time: eventStartTimeSchema,
+    end_time: eventEndTimeSchema,
+    id: zod.string(),
+    reason: zod.string().nullish(),
+    is_recurring: zod.boolean().default(false),
+    recurrence_end_date: zod.date().nullish(),
+    rrule: zod.string().nullish(),
+    created_at: zod.date().nullish(),
+    updated_at: zod.date().nullish(),
+    type: zod.literal('blocked_owned'),
+  })
+  .openapi('OwnedBlockedSlotSchema', {
+    description: 'Blocked slot owned by the user',
+  });
 
 export const VisibleSlotSchema = EventSchema.omit({
   organizer: true,
diff --git a/src/components/calendar.tsx b/src/components/calendar.tsx
index bfd8651..71f326b 100644
--- a/src/components/calendar.tsx
+++ b/src/components/calendar.tsx
@@ -11,6 +11,12 @@ import { useGetApiUserUserCalendar } from '@/generated/api/user/user';
 import { useRouter } from 'next/navigation';
 import { usePatchApiEventEventID } from '@/generated/api/event/event';
 import { useSession } from 'next-auth/react';
+import { UserCalendarSchemaItem } from '@/generated/api/meetup.schemas';
+import { QueryErrorResetBoundary } from '@tanstack/react-query';
+import { ErrorBoundary } from 'react-error-boundary';
+import { Button } from '@/components/ui/button';
+import { fromZodIssue } from 'zod-validation-error/v4';
+import type { $ZodIssue } from 'zod/v4/core';
 
 moment.updateLocale('en', {
   week: {
@@ -24,16 +30,49 @@ const DaDRBCalendar = withDragAndDrop<
     id: string;
     start: Date;
     end: Date;
+    type: UserCalendarSchemaItem['type'];
   },
   {
     id: string;
     title: string;
+    type: UserCalendarSchemaItem['type'];
   }
 >(RBCalendar);
 
 const localizer = momentLocalizer(moment);
 
-export default function Calendar({ userId }: { userId: string }) {
+export default function Calendar({ userId }: { userId?: string }) {
+  return (
+    <QueryErrorResetBoundary>
+      {({ reset }) => (
+        <ErrorBoundary
+          onReset={reset}
+          fallbackRender={({ resetErrorBoundary, error }) => (
+            <div className='flex flex-col items-center justify-center h-full'>
+              There was an error!
+              <p className='text-red-500'>
+                {typeof error === 'string'
+                  ? error
+                  : error.errors
+                      .map((e: $ZodIssue) => fromZodIssue(e).toString())
+                      .join(', ')}
+              </p>
+              <Button onClick={() => resetErrorBoundary()}>Try again</Button>
+            </div>
+          )}
+        >
+          {userId ? (
+            <CalendarWithUserEvents userId={userId} />
+          ) : (
+            <CalendarWithoutUserEvents />
+          )}
+        </ErrorBoundary>
+      )}
+    </QueryErrorResetBoundary>
+  );
+}
+
+function CalendarWithUserEvents({ userId }: { userId: string }) {
   const sesstion = useSession();
   const [currentView, setCurrentView] = React.useState<
     'month' | 'week' | 'day' | 'agenda' | 'work_week'
@@ -41,33 +80,52 @@ export default function Calendar({ userId }: { userId: string }) {
   const [currentDate, setCurrentDate] = React.useState<Date>(new Date());
   const router = useRouter();
 
-  const { data, refetch } = useGetApiUserUserCalendar(userId, {
-    start: moment(currentDate)
-      .startOf(
-        currentView === 'agenda'
-          ? 'month'
-          : currentView === 'work_week'
-            ? 'week'
-            : currentView,
-      )
-      .toISOString(),
-    end: moment(currentDate)
-      .endOf(
-        currentView === 'agenda'
-          ? 'month'
-          : currentView === 'work_week'
-            ? 'week'
-            : currentView,
-      )
-      .toISOString(),
-  });
+  const { data, refetch, error, isError } = useGetApiUserUserCalendar(
+    userId,
+    {
+      start: moment(currentDate)
+        .startOf(
+          currentView === 'agenda'
+            ? 'month'
+            : currentView === 'work_week'
+              ? 'week'
+              : currentView,
+        )
+        .toISOString(),
+      end: moment(currentDate)
+        .endOf(
+          currentView === 'agenda'
+            ? 'month'
+            : currentView === 'work_week'
+              ? 'week'
+              : currentView,
+        )
+        .toISOString(),
+    },
+    {
+      query: {
+        refetchOnWindowFocus: true,
+        refetchOnReconnect: true,
+        refetchOnMount: true,
+      },
+    },
+  );
 
-  const { mutate: patchEvent } = usePatchApiEventEventID();
+  if (isError) {
+    throw error.response?.data || 'Failed to fetch calendar data';
+  }
+
+  const { mutate: patchEvent } = usePatchApiEventEventID({
+    mutation: {
+      throwOnError(error) {
+        throw error.response?.data || 'Failed to update event';
+      },
+    },
+  });
 
   return (
     <DaDRBCalendar
       localizer={localizer}
-      style={{ height: 500 }}
       culture='de-DE'
       defaultView='week'
       components={{
@@ -85,6 +143,7 @@ export default function Calendar({ userId }: { userId: string }) {
           title: event.type === 'event' ? event.title : 'Blocker',
           start: new Date(event.start_time),
           end: new Date(event.end_time),
+          type: event.type,
         })) ?? []
       }
       onSelectEvent={(event) => {
@@ -102,6 +161,7 @@ export default function Calendar({ userId }: { userId: string }) {
       selectable={sesstion.data?.user?.id === userId}
       onEventDrop={(event) => {
         const { start, end, event: droppedEvent } = event;
+        if (droppedEvent.type === 'blocked_private') return;
         const startISO = new Date(start).toISOString();
         const endISO = new Date(end).toISOString();
         patchEvent(
@@ -124,8 +184,13 @@ export default function Calendar({ userId }: { userId: string }) {
       }}
       onEventResize={(event) => {
         const { start, end, event: resizedEvent } = event;
+        if (resizedEvent.type === 'blocked_private') return;
         const startISO = new Date(start).toISOString();
         const endISO = new Date(end).toISOString();
+        if (startISO === endISO) {
+          console.warn('Start and end times are the same, skipping resize.');
+          return;
+        }
         patchEvent(
           {
             eventID: resizedEvent.id,
@@ -147,3 +212,27 @@ export default function Calendar({ userId }: { userId: string }) {
     />
   );
 }
+
+function CalendarWithoutUserEvents() {
+  const [currentView, setCurrentView] = React.useState<
+    'month' | 'week' | 'day' | 'agenda' | 'work_week'
+  >('week');
+  const [currentDate, setCurrentDate] = React.useState<Date>(new Date());
+
+  return (
+    <DaDRBCalendar
+      localizer={localizer}
+      culture='de-DE'
+      defaultView='week'
+      components={{
+        toolbar: CustomToolbar,
+      }}
+      onView={setCurrentView}
+      view={currentView}
+      date={currentDate}
+      onNavigate={(date) => {
+        setCurrentDate(date);
+      }}
+    />
+  );
+}
diff --git a/src/components/custom-toolbar.css b/src/components/custom-toolbar.css
index c55d47a..8f8d1f6 100644
--- a/src/components/custom-toolbar.css
+++ b/src/components/custom-toolbar.css
@@ -109,5 +109,5 @@
 }
 
 .datepicker-box {
-  z-index: 9999;
+  z-index: 5;
 }
diff --git a/yarn.lock b/yarn.lock
index 234ff57..74ff1df 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -156,7 +156,7 @@ __metadata:
   languageName: node
   linkType: hard
 
-"@babel/runtime@npm:^7.13.8, @babel/runtime@npm:^7.20.7, @babel/runtime@npm:^7.3.1, @babel/runtime@npm:^7.6.3, @babel/runtime@npm:^7.8.7":
+"@babel/runtime@npm:^7.12.5, @babel/runtime@npm:^7.13.8, @babel/runtime@npm:^7.20.7, @babel/runtime@npm:^7.3.1, @babel/runtime@npm:^7.6.3, @babel/runtime@npm:^7.8.7":
   version: 7.27.6
   resolution: "@babel/runtime@npm:7.27.6"
   checksum: 10c0/89726be83f356f511dcdb74d3ea4d873a5f0cf0017d4530cb53aa27380c01ca102d573eff8b8b77815e624b1f8c24e7f0311834ad4fb632c90a770fda00bd4c8
@@ -7730,6 +7730,7 @@ __metadata:
     react-datepicker: "npm:^8.4.0"
     react-day-picker: "npm:^9.7.0"
     react-dom: "npm:^19.0.0"
+    react-error-boundary: "npm:^6.0.0"
     react-hook-form: "npm:^7.56.4"
     sonner: "npm:^2.0.5"
     swagger-ui-react: "npm:^5.24.1"
@@ -7740,6 +7741,7 @@ __metadata:
     tw-animate-css: "npm:1.3.4"
     typescript: "npm:^5.8.3"
     zod: "npm:^3.25.60"
+    zod-validation-error: "npm:^3.5.2"
   languageName: unknown
   linkType: soft
 
@@ -9004,6 +9006,17 @@ __metadata:
   languageName: node
   linkType: hard
 
+"react-error-boundary@npm:^6.0.0":
+  version: 6.0.0
+  resolution: "react-error-boundary@npm:6.0.0"
+  dependencies:
+    "@babel/runtime": "npm:^7.12.5"
+  peerDependencies:
+    react: ">=16.13.1"
+  checksum: 10c0/1914d600dee95a14f14af4afe9867b0d35c26c4f7826d23208800ba2a99728659029aad60a6ef95e13430b4d79c2c4c9b3585f50bf508450478760d2e4e732d8
+  languageName: node
+  linkType: hard
+
 "react-hook-form@npm:^7.56.4":
   version: 7.58.1
   resolution: "react-hook-form@npm:7.58.1"
@@ -11274,6 +11287,15 @@ __metadata:
   languageName: node
   linkType: hard
 
+"zod-validation-error@npm:^3.5.2":
+  version: 3.5.2
+  resolution: "zod-validation-error@npm:3.5.2"
+  peerDependencies:
+    zod: ^3.25.0
+  checksum: 10c0/da50926ec91c7ad2880bacc5010a53c42de58f73f7c4629baad8132695c4daf74dd68620787198da81aca85134471182ed4c566b5fc9bc5349aefd8540946d57
+  languageName: node
+  linkType: hard
+
 "zod@npm:^3.25.60":
   version: 3.25.67
   resolution: "zod@npm:3.25.67"