Missing Calendar entries

I have two users who are experiencing similar issues with Outlook 2003.
One has a regular occurence meeting which completely disappeared from her calendar, but not the other attendees calendars.
The other user has had attendees disapearing from her list despite the printed record of the event showing all attendees. The attendees also loose the record off their calendars too.
We are running Office 2k3 SP3 and Windows server2k3