Outlook conflict errors when updating or cancelling meetings

When you update or cancel a meeting item in Outlook Desktop you see a conflict error. 

“One or more items in the folder you synchronized do not match. To resolve the conflicts, open the items, and then try this operation again.”

This issue happens when there is a local conflict of the calendar item in Outlook Desktop. The server copy of the calendar item does not have a conflict. 

If you are prompted with the Conflict Message dialog close it out. Using this dialog may not fully address the issue. 

The conflict issue is only in Outlook Desktop and only on the machine that the conflict is found. It is not on other machines or on recipients’ copies of the meetings. 

Microsoft Article re the problem

https://support.microsoft.com/en-us/office/outlook-shows-conflict-errors-when-updating-or-cancelling-meetings-69c26227-40ef-4377-8f12-1749fcaad2ad

Workaround 1:

To mitigate the issue, you can use the Clear Offline Items for your calendar. This step clears the calendar items in the Outlook store (OST) on your local machine. 

To clear offline Calendar items, follow these steps: 

1. Open the Calendar pane in Outlook, and right-click the Calendar folder.

2. Select Properties.

3. On the General tab, select Clear Offline Items.

4. Select OK.

After you clear offline items, Outlook will re-sync the calendar and repopulate your calendar folder with the calendar items on the server. 

These steps do not fix duplicates. Meetings that will be fixed by these steps are those indicated by a diamond. 

Example:

Workaround 2:

Make the meeting updates in Outlook Web Access (OWA) or use New Outlook. The conflict does not occur when updating or cancelling the meeting in OWA or New Outlook. The conflict issue is only in Outlook Desktop and only on the machine that the conflict is found. It is not on other machines or on recipients’ copies of the meetings. 

Workaround 3:

This step is primarily for use by IT Support Engineers

If you got the Conflict Message dialog opening a meeting item and selected Keep All, then multiple duplicate copies of the meeting were created. If there are too many copies to easily cancel from Outlook Desktop, you can use Calcheck to remove the duplicates. 

To use CalCheck to remove duplicate items on the organizers calendar created by incident EX800425, use the following steps:

1. Download CalCheck. Download Calendar Checking Tool for Outlook.
   For more information about Calcheck usage, please go to Information about the Calendar Checking Tool for Outlook (CalCheck).
   

2. On the organizers machine, create a folder c:\calcheck and extract the CalCheck zip file to this folder (right click the zip file and select Extract All..).
   
   

3. In the folder c:\calcheck, locate the calcheck.cfg and open it to edit in Notepad. Make the following changes and then save from Notepad:
   
   To specifically identify and remove the duplicate items created by the incident, set DupGlobalObjectIDs=true and all other tests to false and save the calcheck.cfg file.
   
   You can also open Notepad first and drag the calcheck.cfg into Notepad

4. Close Outlook and Excel.
   
   

5. Open a Command Prompt window and change the directory to c:\calcheck (cd \calcheck). Type calcheck.exe and press Enter. You will be prompted for the Outlook profile with the duplicates. Pick the profile and select OK.
   
   

6. Use Windows Explorer to go to the folder c:\calcheck and open the CalCheckErr.csv. It should list the duplicated items.
   
   Example:
    
   

7. Close Excel.
   
   

8. If you are satisfied with the list, you can now remove those duplicates.
   The duplicates will be moved to a new folder called Calcheck in the Outlook folder list.
   
   Go back to the Command Prompt window and type the following command and press Enter. Make sure Outlook Desktop is closed before you run the command. 

             
   

   C:\calcheck>calcheck.exe -F -R
   

9. In the profile picker window, pick the profile you need to remove the duplicate calendar items.
   
   

10. The command prompt window will show as below once it is completed.
    
    
    Before you close it, use Windows Explorer and go to the C:\calcheck folder and open the Calcheck.log to make sure it says it is finished and shows the current time at the bottom of the log. If completed, close the command prompt window. It will not close by itself. 

                

    Finish: 07/05/2024 11:53:30AM 

    Finished processing mailbox /o=ExchangeLabs/ou=Exchange Administrative Group (FYDIBOHF23SPDLT)/cn=Recipients/cn=b6121eb9ed4ea0822d864549e4f59d-manageruser  

11. The "calcheck.exe -F -R" command created a folder in your Outlook folder list that has the duplicate items. If after some time you confirm the duplicate issue is resolved, you can delete that folder.
     

12. If the duplicate items are not removed, close Outlook and run the command again and allow the command prompt window a couple minutes to complete the task.