[GH-ISSUE #293] 403 Forbidden error when syncing to Open Xchange (OX) server with some events #1184

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opened 2026-03-14 00:34:29 +03:00 by kerem · 4 comments

kerem commented 2026-03-14 00:34:29 +03:00

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Originally created by @argoneus on GitHub (Oct 29, 2020).
Original GitHub issue: https://github.com/aluxnimm/outlookcaldavsynchronizer/issues/293

Hello,

I'm experiencing issues syncing events to an Open Xchange server. The list of events with errors varies, but the error is the same for all events. Also, I'm seeing the error with both single occurrence and recurring event items. Below is the error:

CalDavSynchronizer.DataAccess.WebDavClientException: Response status code does not indicate success: '403' ('Forbidden'). Message:

   at CalDavSynchronizer.DataAccess.HttpClientBasedClient.WebDavClient.<EnsureSuccessStatusCode>d__10.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.ValidateEnd(Task task)
   at CalDavSynchronizer.DataAccess.HttpClientBasedClient.WebDavClient.<ExecuteWebDavRequest>d__9.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at CalDavSynchronizer.DataAccess.HttpClientBasedClient.WebDavClient.<ExecuteWebDavRequestAndReturnResponseHeaders>d__8.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at CalDavSynchronizer.DataAccess.CalDavDataAccess.<TryUpdateEntity>d__28.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at CalDavSynchronizer.Implementation.CalDavRepository`1.<TryUpdate>d__16.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at CalDavSynchronizer.Implementation.CalDavRepository`1.<TryUpdate>d__16.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.ValidateEnd(Task task)
   at GenSync.EntityRepositories.BatchEntityRepositoryAdapter`4.<PerformOperations>d__3.MoveNext()

Details:
Windows 10 (19041.572)
Outlook 365 Version 2007 (Build 13029.20308)
CalDav Synchronizer 3.8.2

This appears related to https://github.com/aluxnimm/outlookcaldavsynchronizer/issues/292 but is a different error. It's not limited to recurring events (as is the case in #292 ), but affects single events as well.

Originally created by @argoneus on GitHub (Oct 29, 2020). Original GitHub issue: https://github.com/aluxnimm/outlookcaldavsynchronizer/issues/293 Hello, I'm experiencing issues syncing events to an Open Xchange server. The list of events with errors varies, but the error is the same for all events. Also, I'm seeing the error with both single occurrence and recurring event items. Below is the error: ``` CalDavSynchronizer.DataAccess.WebDavClientException: Response status code does not indicate success: '403' ('Forbidden'). Message: at CalDavSynchronizer.DataAccess.HttpClientBasedClient.WebDavClient.<EnsureSuccessStatusCode>d__10.MoveNext() --- End of stack trace from previous location where exception was thrown --- at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) at System.Runtime.CompilerServices.TaskAwaiter.ValidateEnd(Task task) at CalDavSynchronizer.DataAccess.HttpClientBasedClient.WebDavClient.<ExecuteWebDavRequest>d__9.MoveNext() --- End of stack trace from previous location where exception was thrown --- at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) at CalDavSynchronizer.DataAccess.HttpClientBasedClient.WebDavClient.<ExecuteWebDavRequestAndReturnResponseHeaders>d__8.MoveNext() --- End of stack trace from previous location where exception was thrown --- at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) at CalDavSynchronizer.DataAccess.CalDavDataAccess.<TryUpdateEntity>d__28.MoveNext() --- End of stack trace from previous location where exception was thrown --- at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) at CalDavSynchronizer.Implementation.CalDavRepository`1.<TryUpdate>d__16.MoveNext() --- End of stack trace from previous location where exception was thrown --- at CalDavSynchronizer.Implementation.CalDavRepository`1.<TryUpdate>d__16.MoveNext() --- End of stack trace from previous location where exception was thrown --- at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) at System.Runtime.CompilerServices.TaskAwaiter.ValidateEnd(Task task) at GenSync.EntityRepositories.BatchEntityRepositoryAdapter`4.<PerformOperations>d__3.MoveNext() ``` Details: Windows 10 (19041.572) Outlook 365 Version 2007 (Build 13029.20308) CalDav Synchronizer 3.8.2 This appears related to https://github.com/aluxnimm/outlookcaldavsynchronizer/issues/292 but is a different error. It's not limited to recurring events (as is the case in #292 ), but affects single events as well.

kerem commented 2026-03-14 00:34:35 +03:00

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@swalterfub commented on GitHub (Mar 11, 2022):

I have a similar issue, but only when I change existing events.
Windows 10 21H1
Outlook 2021 Version 2202
Caldav Synchronizer 4.2.0.0

CalDavSynchronizer.DataAccess.WebDavClientException: Response status code does not indicate success: '403' ('Forbidden'). Message:

   at CalDavSynchronizer.DataAccess.HttpClientBasedClient.WebDavClient.<EnsureSuccessStatusCode>d__10.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.ValidateEnd(Task task)
   at CalDavSynchronizer.DataAccess.HttpClientBasedClient.WebDavClient.<ExecuteWebDavRequest>d__9.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at CalDavSynchronizer.DataAccess.HttpClientBasedClient.WebDavClient.<ExecuteWebDavRequestAndReturnResponseHeaders>d__8.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at CalDavSynchronizer.DataAccess.CalDavDataAccess.<TryUpdateEntity>d__28.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at CalDavSynchronizer.Implementation.CalDavRepository`1.<TryUpdate>d__16.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at CalDavSynchronizer.Implementation.CalDavRepository`1.<TryUpdate>d__16.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.ValidateEnd(Task task)
   at GenSync.EntityRepositories.BatchEntityRepositoryAdapter`4.<PerformOperations>d__3.MoveNext()

<!-- gh-comment-id:1065120741 --> @swalterfub commented on GitHub (Mar 11, 2022): I have a similar issue, but only when I change existing events. Windows 10 21H1 Outlook 2021 Version 2202 Caldav Synchronizer 4.2.0.0 ``` CalDavSynchronizer.DataAccess.WebDavClientException: Response status code does not indicate success: '403' ('Forbidden'). Message: at CalDavSynchronizer.DataAccess.HttpClientBasedClient.WebDavClient.<EnsureSuccessStatusCode>d__10.MoveNext() --- End of stack trace from previous location where exception was thrown --- at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) at System.Runtime.CompilerServices.TaskAwaiter.ValidateEnd(Task task) at CalDavSynchronizer.DataAccess.HttpClientBasedClient.WebDavClient.<ExecuteWebDavRequest>d__9.MoveNext() --- End of stack trace from previous location where exception was thrown --- at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) at CalDavSynchronizer.DataAccess.HttpClientBasedClient.WebDavClient.<ExecuteWebDavRequestAndReturnResponseHeaders>d__8.MoveNext() --- End of stack trace from previous location where exception was thrown --- at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) at CalDavSynchronizer.DataAccess.CalDavDataAccess.<TryUpdateEntity>d__28.MoveNext() --- End of stack trace from previous location where exception was thrown --- at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) at CalDavSynchronizer.Implementation.CalDavRepository`1.<TryUpdate>d__16.MoveNext() --- End of stack trace from previous location where exception was thrown --- at CalDavSynchronizer.Implementation.CalDavRepository`1.<TryUpdate>d__16.MoveNext() --- End of stack trace from previous location where exception was thrown --- at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) at System.Runtime.CompilerServices.TaskAwaiter.ValidateEnd(Task task) at GenSync.EntityRepositories.BatchEntityRepositoryAdapter`4.<PerformOperations>d__3.MoveNext() ```

kerem commented 2026-03-14 00:34:40 +03:00

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@frankneumann commented on GitHub (Mar 23, 2022):

Since we migrated to OpenExchange version 7.10.5-Rev39 I get for certain events also the above mentioned error message.
Windows 10 21H2
Outlook 2021 Version 2203
Caldav Synchronizer 4.2.0.0

Does anybody know whether there is a workaround or fix for this problem?

CalDavSynchronizer.DataAccess.WebDavClientException: Response status code does not indicate success: '403' ('Forbidden'). Message:

bei CalDavSynchronizer.DataAccess.HttpClientBasedClient.WebDavClient.d__10.MoveNext()
--- Ende der Stapelüberwachung vom vorhergehenden Ort, an dem die Ausnahme ausgelöst wurde ---
bei System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
bei System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
bei System.Runtime.CompilerServices.TaskAwaiter.ValidateEnd(Task task)
bei CalDavSynchronizer.DataAccess.HttpClientBasedClient.WebDavClient.d__9.MoveNext()
--- Ende der Stapelüberwachung vom vorhergehenden Ort, an dem die Ausnahme ausgelöst wurde ---
bei System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
bei System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
bei CalDavSynchronizer.DataAccess.HttpClientBasedClient.WebDavClient.d__8.MoveNext()
--- Ende der Stapelüberwachung vom vorhergehenden Ort, an dem die Ausnahme ausgelöst wurde ---
bei System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
bei System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
bei CalDavSynchronizer.DataAccess.CalDavDataAccess.d__28.MoveNext()
--- Ende der Stapelüberwachung vom vorhergehenden Ort, an dem die Ausnahme ausgelöst wurde ---
bei System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
bei System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
bei CalDavSynchronizer.Implementation.CalDavRepository1.d__16.MoveNext() --- Ende der Stapelüberwachung vom vorhergehenden Ort, an dem die Ausnahme ausgelöst wurde --- bei CalDavSynchronizer.Implementation.CalDavRepository1.d__16.MoveNext()
--- Ende der Stapelüberwachung vom vorhergehenden Ort, an dem die Ausnahme ausgelöst wurde ---
bei System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
bei System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
bei System.Runtime.CompilerServices.TaskAwaiter.ValidateEnd(Task task)
bei GenSync.EntityRepositories.BatchEntityRepositoryAdapter`4.d__3.MoveNext()

<!-- gh-comment-id:1076406970 --> @frankneumann commented on GitHub (Mar 23, 2022): Since we migrated to OpenExchange version 7.10.5-Rev39 I get for certain events also the above mentioned error message. Windows 10 21H2 Outlook 2021 Version 2203 Caldav Synchronizer 4.2.0.0 Does anybody know whether there is a workaround or fix for this problem? CalDavSynchronizer.DataAccess.WebDavClientException: Response status code does not indicate success: '403' ('Forbidden'). Message: bei CalDavSynchronizer.DataAccess.HttpClientBasedClient.WebDavClient.d__10.MoveNext() --- Ende der Stapelüberwachung vom vorhergehenden Ort, an dem die Ausnahme ausgelöst wurde --- bei System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) bei System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) bei System.Runtime.CompilerServices.TaskAwaiter.ValidateEnd(Task task) bei CalDavSynchronizer.DataAccess.HttpClientBasedClient.WebDavClient.d__9.MoveNext() --- Ende der Stapelüberwachung vom vorhergehenden Ort, an dem die Ausnahme ausgelöst wurde --- bei System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) bei System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) bei CalDavSynchronizer.DataAccess.HttpClientBasedClient.WebDavClient.d__8.MoveNext() --- Ende der Stapelüberwachung vom vorhergehenden Ort, an dem die Ausnahme ausgelöst wurde --- bei System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) bei System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) bei CalDavSynchronizer.DataAccess.CalDavDataAccess.d__28.MoveNext() --- Ende der Stapelüberwachung vom vorhergehenden Ort, an dem die Ausnahme ausgelöst wurde --- bei System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) bei System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) bei CalDavSynchronizer.Implementation.CalDavRepository1.<TryUpdate>d__16.MoveNext() --- Ende der Stapelüberwachung vom vorhergehenden Ort, an dem die Ausnahme ausgelöst wurde --- bei CalDavSynchronizer.Implementation.CalDavRepository1.d__16.MoveNext() --- Ende der Stapelüberwachung vom vorhergehenden Ort, an dem die Ausnahme ausgelöst wurde --- bei System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) bei System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) bei System.Runtime.CompilerServices.TaskAwaiter.ValidateEnd(Task task) bei GenSync.EntityRepositories.BatchEntityRepositoryAdapter`4.d__3.MoveNext()

kerem commented 2026-03-14 00:34:45 +03:00

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@aluxnimm commented on GitHub (Mar 24, 2022):

We would need the ics file from the server and the export of the outlook appointment that causes this 403 error, you will find both in the sync report whne clicking on server id/outlook id.

<!-- gh-comment-id:1077399436 --> @aluxnimm commented on GitHub (Mar 24, 2022): We would need the ics file from the server and the export of the outlook appointment that causes this 403 error, you will find both in the sync report whne clicking on server id/outlook id.

kerem commented 2026-03-14 00:34:50 +03:00

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@frankneumann commented on GitHub (Mar 24, 2022):

OK - here we go. The server and the outlook events as ics data
[Diskussion KMU Innovativ Pro
Diskussion KMU Innovativ Produktionsforschung Server.zip
duktionsforschung Outlook.zip](https://github.com/aluxnimm/outlookcaldavsynchronizer/files/8341114/Diskussion.KMU.Innovativ.Produktionsforschung.Outlook.zip)
.

<!-- gh-comment-id:1077540185 --> @frankneumann commented on GitHub (Mar 24, 2022): OK - here we go. The server and the outlook events as ics data [Diskussion KMU Innovativ Pro [Diskussion KMU Innovativ Produktionsforschung Server.zip](https://github.com/aluxnimm/outlookcaldavsynchronizer/files/8341118/Diskussion.KMU.Innovativ.Produktionsforschung.Server.zip) duktionsforschung Outlook.zip](https://github.com/aluxnimm/outlookcaldavsynchronizer/files/8341114/Diskussion.KMU.Innovativ.Produktionsforschung.Outlook.zip) .

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