Old reminders appears periodical

[Eran]

Hi,
I'm outlook 2000 user, using offline feature on my
laptop. Since my company upgraded our exchange server,
every week old reminders suddenly appears in my outlook
(online mode). After I dismiss them, again, a week after
(every Sunday) they all appear again.
What is the problem?
How I can get rid of these old reminders not activated
again after a week?

Thanks