diff --git a/backend/src/jobs/notification-generation.job.ts b/backend/src/jobs/notification-generation.job.ts
index 659a0c1..87b5360 100644
--- a/backend/src/jobs/notification-generation.job.ts
+++ b/backend/src/jobs/notification-generation.job.ts
@@ -12,6 +12,7 @@
 
 import pool from '../config/database';
 import notificationService from '../services/notification.service';
+import nextcloudService from '../services/nextcloud.service';
 import logger from '../utils/logger';
 
 const INTERVAL_MS = 15 * 60 * 1000; // 15 minutes
@@ -28,6 +29,7 @@ export async function runNotificationGeneration(): Promise<void> {
     await generateAtemschutzNotifications();
     await generateVehicleNotifications();
     await generateEquipmentNotifications();
+    await generateNextcloudTalkNotifications();
     await notificationService.deleteOldRead();
   } catch (error) {
     logger.error('NotificationGenerationJob: unexpected error', {
@@ -234,6 +236,56 @@ async function generateEquipmentNotifications(): Promise<void> {
   }
 }
 
+// ---------------------------------------------------------------------------
+// 4. Nextcloud Talk unread messages → per-user notifications
+// ---------------------------------------------------------------------------
+
+async function generateNextcloudTalkNotifications(): Promise<void> {
+  const usersResult = await pool.query(`
+    SELECT id, nextcloud_login_name, nextcloud_app_password
+    FROM users
+    WHERE is_active = TRUE
+      AND nextcloud_login_name IS NOT NULL
+      AND nextcloud_app_password IS NOT NULL
+  `);
+
+  for (const user of usersResult.rows) {
+    try {
+      const { conversations } = await nextcloudService.getConversations(
+        user.nextcloud_login_name,
+        user.nextcloud_app_password,
+      );
+
+      for (const conv of conversations) {
+        if (conv.unreadMessages <= 0) continue;
+        await notificationService.createNotification({
+          user_id:   user.id,
+          typ:       'nextcloud_talk',
+          titel:     conv.displayName,
+          nachricht: `${conv.unreadMessages} ungelesene Nachrichten`,
+          schwere:   'info',
+          link:      conv.url,
+          quell_id:  conv.token,
+          quell_typ: 'nextcloud_talk',
+        });
+      }
+    } catch (error: any) {
+      if (error?.code === 'NEXTCLOUD_AUTH_INVALID') {
+        await pool.query(
+          `UPDATE users SET nextcloud_login_name = NULL, nextcloud_app_password = NULL WHERE id = $1`,
+          [user.id],
+        );
+        logger.warn('NotificationGenerationJob: cleared invalid Nextcloud credentials', { userId: user.id });
+        continue;
+      }
+      logger.error('NotificationGenerationJob: generateNextcloudTalkNotifications failed for user', {
+        userId: user.id,
+        error,
+      });
+    }
+  }
+}
+
 // ---------------------------------------------------------------------------
 // Job lifecycle
 // ---------------------------------------------------------------------------
diff --git a/frontend/src/pages/Kalender.tsx b/frontend/src/pages/Kalender.tsx
index dcf1807..90ae8c3 100644
--- a/frontend/src/pages/Kalender.tsx
+++ b/frontend/src/pages/Kalender.tsx
@@ -68,7 +68,7 @@ import {
 } from '@mui/icons-material';
 import { useNavigate } from 'react-router-dom';
 import DashboardLayout from '../components/dashboard/DashboardLayout';
-import { toGermanDate, toGermanDateTime, fromGermanDate, fromGermanDateTime } from '../utils/dateInput';
+import { toGermanDate, toGermanDateTime, fromGermanDate, fromGermanDateTime, isValidGermanDate, isValidGermanDateTime } from '../utils/dateInput';
 import { useAuth } from '../contexts/AuthContext';
 import { useNotification } from '../contexts/NotificationContext';
 import { trainingApi } from '../services/training';
@@ -1187,6 +1187,27 @@ function VeranstaltungFormDialog({
       notification.showError('Titel ist erforderlich');
       return;
     }
+
+    // Date validation
+    const vonDate = new Date(form.datum_von);
+    const bisDate = new Date(form.datum_bis);
+    if (isNaN(vonDate.getTime())) {
+      notification.showError(`Ungültiges Datum Von (Format: ${form.ganztaegig ? '01.03.2025' : '01.03.2025 18:00'})`);
+      return;
+    }
+    if (isNaN(bisDate.getTime())) {
+      notification.showError(`Ungültiges Datum Bis (Format: ${form.ganztaegig ? '01.03.2025' : '01.03.2025 18:00'})`);
+      return;
+    }
+    if (bisDate < vonDate) {
+      notification.showError('Datum Bis muss nach Datum Von liegen');
+      return;
+    }
+    if (wiederholungAktiv && wiederholungBis && !isValidGermanDate(wiederholungBis)) {
+      notification.showError('Ungültiges Datum für Wiederholung Bis (Format: 01.03.2025)');
+      return;
+    }
+
     setLoading(true);
     try {
       const createPayload: CreateVeranstaltungInput = {
@@ -1289,6 +1310,7 @@ function VeranstaltungFormDialog({
                 : fromDatetimeLocal(raw);
               handleChange('datum_von', iso);
             }}
+            helperText={form.ganztaegig ? 'Format: 01.03.2025' : 'Format: 01.03.2025 18:00'}
             InputLabelProps={{ shrink: true }}
             fullWidth
           />
@@ -1307,6 +1329,7 @@ function VeranstaltungFormDialog({
                 : fromDatetimeLocal(raw);
               handleChange('datum_bis', iso);
             }}
+            helperText={form.ganztaegig ? 'Format: 01.03.2025' : 'Format: 01.03.2025 18:00'}
             InputLabelProps={{ shrink: true }}
             fullWidth
           />
@@ -2190,6 +2213,13 @@ export default function Kalender() {
               </DialogContent>
               <DialogActions>
                 <Button onClick={() => setIcalEventOpen(false)}>Schließen</Button>
+                <Button
+                  variant="outlined"
+                  startIcon={<FileDownloadIcon />}
+                  onClick={() => window.open(icalEventUrl, '_blank')}
+                >
+                  Herunterladen
+                </Button>
               </DialogActions>
             </Dialog>
           </Box>
@@ -2678,6 +2708,13 @@ export default function Kalender() {
               </DialogContent>
               <DialogActions>
                 <Button onClick={() => setIcalBookingOpen(false)}>Schließen</Button>
+                <Button
+                  variant="outlined"
+                  startIcon={<FileDownloadIcon />}
+                  onClick={() => window.open(icalBookingUrl, '_blank')}
+                >
+                  Herunterladen
+                </Button>
               </DialogActions>
             </Dialog>
           </Box>