When this error occurred, the user could not open their own calendar folder on the Exchange server, although it was openable in OWA. Creating a new MAPI profile for Outlook resolved this issue.
From a newsgroup post: "If you are getting this message here are the steps to fix it:
1. Bring up your Calendar.
2. Click on "View" at the top of the window.
3. Click on "Arrange By".
4. Click on "Current View".
5. Click on "By Category".
6. Click on all the reminders within the dates that you started having the problem. When you get the one that brings up the error message, delete it (you might want to write it down if you want to re-enter the reminder). You might have more than one message causing the problem so I would continue checking the reminders just in case.
7. When you are done, to bring the view back to normal (normal for me) click on "View".
8. Click on "Arrange By".
9. Click on "Current View" at the bottom of the menu.
10. Click on "Day/Week/Month" and you should be back to the Default setting".