Sometimes, if an Exchange calendar is shared by multiple people, a deleted appointment may spontaneously reappear for no apparent reason. This problem usually doesn't extend to include calendar items not being saved correctly, but merely involves deleted items reappearing on their own.
Here's why this happens: If Outlook users are allowed to set up their own local .OST files to store mail and appointments, sometimes the data can be corrupted locally and bad data will be sent back to the server when a resynchronization takes place. What one user deleted can wind up being restored, quite by accident, by another user.
There are two ways to get around this. One is to stop using local .OST files, and to simply store all Outlook information on the Exchange server itself. This may not be practical, however, especially if the local files are used to hold a good deal more data than can be managed efficiently on the server itself. But if the appointment problem is happening a great deal, and it is economically feasible to store the data on the server, then perhaps some thought should be given towards doing that.
The other option is to delete the offending user's .OST file and recreate it from a backup copy. This generally solves the corruption problem at least temporarily, but if a user's data keeps getting corrupted, then there may be something wrong with the computer itself.
Serdar Yegulalp is the editor of the Windows 2000 Power Users Newsletter.