this meeting is not in the calendar it may have been moved or deleted

Hello,

I have a user here who is using Outlook 2000 and on many
meetings she received the message "this meeting is not in the calendar
it may have been moved or deleted" when she try's to accept the meeting
receives "You have changed one or more of the recurrences of this item,
and this instance no longer exists Close any open items and try again".
No matter what she does she can not accept the meeting.

Can anyone provide any help/idea's?

thanks,

Marc