Outlook Reminders appear after dismissal

In Outlook 2000 a user is having meeting reminders reappear after he dismisses them. After a while they build up until he has lots of reminders to dismiss everytime he opens Outlook.
We have tried un-ticking Process Meeting Reminders automatically,we have also tried the /cleanreminders switch. We can delete the appointment but that is not practical. Any help would be gratefully appreciated – it is driving him crazy!