I deleted a calendar appointment about three weeks ago.  
For some reason the reminder for it will just not go
away.  I dismiss the reminder and it is gone,
temoporarily.  Whenever I restart outlook it pops up the
reminder again.  If I try to open  the item from the
reminder dialog box I get the following error message

"Cannot open the item for this reminder.  Unknown Error"

I use multiple clients on different computers with the
same result. (WinXP, WinNT, Office 2002, Office 2003)  My
guess is that it is a bug on the Exchange server.

Any clues?  I'm getting tired of being reminded that I'm X
weeks late for a meeting that I attended X weeks ago!