Disappearing meetings

We are running Exchange 2000 Enterprise SP3 on Windows 2000 Advanced Server SP4. Our Outlook version is XP, installed with the full Office XP suite, on clients with Windows 2000 Professional OS. Recently we've had several complaints that when recurring meetings are rescheduled, the attendees' calendars are not updated after they accept the meeting update. All calendars involved are handled by delegates, both for scheduling and accepting/rejecting meeting invitations and updates. One delegate said that after she accepted the updated meeting schedule, the meeting appeared on her boss' calendar briefly, but later it was no longer there -- it "disappeared." This has happened to more than one person and has caused problems with people missing meetings. Does this indicate a problem with the Exchange database? Any suggestions on how to fix this would be appreciated. I've seen similar problems posted on different forums, but no one answers them.