I'm researching the same problem and here is what I found.
"I'd close Outlook, use the Mail applet in Control Panel to remove the IMAP account, re-add the IMAP account, and then restart Outlook."
or
"
1. Close Outlook
2. Go to /program files/Microsoft Office/Office 12 and run scan SCANPST.EXE as Administrator.
3. You will find your PST file (if you have not changed it) in YOU/AppData/Local/Microsoft/Outlook/ (You can check this location by using FILE->Manage Data Files in outlook but don't forget to close it after).
4. Allow the file to scan and fix the issues.
5. Restart Outlook.
"
You could also check your files online, mostly calendar events. Because they can be corrupted, but there is no way to check how they are really. You can check outlook online if you have that, I don't, and if there is a calendar event that you have on your computer and not online then that is the corrupted one and once you delete it everything will be fine.
If you have solved this problem already please tell me how you did it.