How to check for calendar corruption.

A corrupt calendar item can reallly mess-up a custom application and even some very seasoned applications.  If there is a corrupt item/items, then those should be cleared-up ASAP before trying to do some sort of code work-around.   If you are suspecting calendar corruption, you should consider using one of the following.


CalCheck - The Outlook Calendar

Exchange 2010 has a feature called the Calendar Repair Assistant:

Understanding Calendar repair

Exchange 2010 Calendar Repair – Part 1

Exchange 2010 Calendar Repair – Part 2

Steve’s PowerPoof:

Poof Your Calendar - Really!

Checking if a meeting has a duplicate UID with MFCMapi:

Its possible to have a duplicate UID accross meetings in a calendar, thats bad.  UID's in meetings need to be unique.  The problem is that its up to the client or client's API to generate a UID. Meeting updates sent by mail are matched using the UID, so if there is a duplicate Exchange may not pick the correct meeting to update.

One way to check for dupliate UIDs in a calendar is to use MFCMAPI to navigate to the calendar folder, drill down to the items, scroll to the right until you see the UID property and then sort the list.  From there, you can scroll down until you see the UID of your meeting and check for entries above and below it to see if they have the same UID - if you do, then pick one for removal.

Comments (9)
  1. Vivian says:

    Hi Dan,

    Thanks for posting this. Would you happen to know of any utilities that can check for calendar corruption in Outlook 2013?



  2. Webdav101 says:

    You should be looking at Calcheck – which is noted at the top.  Here is more info on Calcheck:…/calcheck-the-outlook-calendar-checking-tool.aspx

  3. Fernando says:

    Hi everyone.

    My problem was with reminders only. I kept getting old reminders even after I dismissed them.

    Some error message with "cannot turn off the reminder" phrase appeared.

    I've solved it by starting outlook with the following command line:

    outlook /cleanreminders

    My outlook version is 2010.

    Hope this help someone.



  4. SP says:

    outlook /cleanreminders worked for me.

    Thank you

  5. Shane Mork says:


    I also faced calendar issue in MS Outlook 2010 email client but resolved successfully through manual detection of corrupt calendar item.  At this moment, there is a possibility to appear a dialogue box with message “corrupt entry cannot be deleted”.  In this situation, it becomes necessary to repair affected zone of Outlook PST file.

    To know other issues, must read:

  6. Ann says:

    I got a message when opening my email file, saying it could not be opened due to a corrupt calendar. I don't know what to do. I am your typical little old lady who knows nothing about what's under the hood of my car, nor do I understand how the computer does what it does. I've Googled "corrupt calendar" but can't make any sense out of the complex tech-talk telling me how to fix it. Could anyone help, preferably in words of one or two syllables?? Any ideas about how to get this fixed would also be welcome. Thanks so much!

  7. Ann says:

    In my post a few minutes ago, I forgot to say I never use Calendar and don't know how to access it or anything else about it. I just want this email problem to go away. I don't care about Calendar, as I am still pretty much living in the 19th century and quite happy there!

  8. Webdav101 says:

    Ahhh just removed another advertisement posted to my blog.   Please don't post advertisements to this blog.

  9. Andy says:

    Thank you so much!! The MFCMAPI trick (finding the offending Calendar entry listed multiple times in the server Calendar entry file and deleting them) resolved an extremely frustrating problem for me.

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