Overview

When using the CalDAV Synchronizer plugin in Outlook to sync calendars with Kerio Connect, a COMException (0x8004010F): The attempted operation failed. An object could not be found error can appear during synchronization. This error is a client-side failure — Outlook is unable to save a specific calendar item locally, typically a recurring meeting or recurrence exception that has become stuck in the plugin's sync cache.

This article applies to Kerio Connect users running the CalDAV Synchronizer plugin in Windows Outlook (any supported version). It explains why the error occurs and how to clear the corrupted sync state so that synchronization resumes normally.

In This Article

• Symptoms
• Cause
• Resolution
  • Step 1: Clear the sync cache for the affected profile
  • Step 2: Run a fresh sync and verify
• If the Error Persists: Collect Debug Logs
• FAQ

Symptoms

• CalDAV Synchronizer reports an error during calendar sync containing:

  System.Runtime.InteropServices.COMException (0x8004010F): The attempted operation failed. An object could not be found.

• The stack trace includes lines such as:

  Microsoft.Office.Interop.Outlook._AppointmentItem.Save()
  CalDavSynchronizer.Implementation.ComWrappers.AppointmentItemWrapper.SaveAndReload()
  CalDavSynchronizer.Implementation.Events.EventEntityMapper.Map2To1(...)
  CalDavSynchronizer.Implementation.Events.OutlookEventRepository.TryUpdate(...)

• The same error repeats on every sync run without resolving itself.
• Most calendar items sync successfully; only one or a small number of recurring items continue to fail.
• The affected calendar events appear correctly in Kerio Connect Webmail.

Cause

This error originates on the Outlook client side, not on the Kerio Connect server. The CalDAV Synchronizer plugin successfully downloads the calendar item from the server, but Outlook fails when the plugin tries to save it into the local Outlook data store (_AppointmentItem.Save()).

The most common trigger is a recurring event or recurrence exception that is in a corrupt or inconsistent state in the plugin's local sync cache — for example, an item that was previously deleted in Outlook (which generates error 0x8004010A) but whose entry was never removed from the plugin's sync state. On every subsequent run, the plugin attempts to update the same stale item and fails with 0x8004010F.

Because the failure happens during the local write step and not during server communication, standard server-side checks (Calendar folder type markers, Use GlobalAppointmentID for UID attribute) will already pass. The resolution is to clear the plugin's local sync cache.

Resolution

Step 1: Clear the sync cache for the affected profile

1. Open Outlook on the affected workstation.
2. In the Outlook ribbon, click CalDav Synchronizer.
3. Click Synchronization Profiles to open the profile list window.
4. Click the affected sync profile once to select it.
5. In the toolbar at the top of the Synchronization Profiles window, click Clear cache.

Important: Clear cache is a toolbar button at the top of the Synchronization Profiles window. It is not available in the right-click context menu on the profile — the right-click menu opens the cache directory on disk; it does not clear the cache. If you do not see the button, make sure the window is fully open and that a profile is selected.

1. Confirm the cache clear if prompted.
2. Close the Synchronization Profiles window.

Step 2: Run a fresh sync and verify

1. In the Outlook ribbon, click CalDav Synchronizer > Synchronize now, or wait for the next scheduled sync run.
2. After the sync completes, open the Calendar view in Outlook and confirm that events are present and no error is reported.

Note: After clearing the cache, the plugin performs a full initial sync on the next run. This takes longer than a normal incremental sync — the duration depends on how many calendar items are in the mailbox.

If the Error Persists: Collect Debug Logs

If 0x8004010F still appears after clearing the cache, a specific calendar item may be fundamentally corrupt on the server or in Outlook. Collect a debug log to identify which item is failing:

1. In the Outlook ribbon, click CalDav Synchronizer > General Options.
2. Set Log level to DEBUG and click OK.
3. Trigger a sync run and allow the error to reproduce once.
4. Locate and save the log file, found by default at: %APPDATA%\CalDavSynchronizer\log.txt
5. Attach log.txt to your support ticket.
6. Reset the log level to its previous setting after collecting the log.

The debug log identifies the exact CalDAV object UID that is failing, which allows support to determine whether the item needs to be deleted or recreated on the server side.

FAQ

Q1: Will clearing the cache delete my calendar events?
A1: No. Clearing the cache only removes the plugin's local sync state file. Your calendar data remains on the Kerio Connect server and in your Outlook data store. After clearing the cache, the plugin performs a fresh initial sync and re-downloads all events from the server.

Q2: Why does the same error repeat on every sync without resolving itself?
A2: The CalDAV Synchronizer plugin retries any failed item on each sync cycle. If the item's cached state cannot be resolved by a normal incremental sync — because the Outlook-side object it references no longer exists — the error repeats indefinitely until the cache is cleared and the plugin re-establishes clean sync state for that item.

Q3: Is this a Kerio Connect server issue or an Outlook/plugin issue?
A3: For 0x8004010F with this stack trace, the failure is on the Outlook client side — specifically when the plugin tries to save a calendar item into Outlook's local data store. You can confirm this by checking whether the affected event is visible and correct in Kerio Connect Webmail. If Webmail shows the event normally, the server data is intact and the fix is to clear the plugin cache as described above.

See also: Synchronizing Calendars using Outlook CalDAV Synchronizer plugin