There is a known incompatiblity between Outlook 2000 and later versions related to reminders on meeting requests sent in iCalendar (aka iCal) format. To resolve this issue, do one of the following:
-- Contact Microsoft Product Support Services to obtain the Outlook 2000 post-SP3 hotfix described in this article:
http://support.microsoft.com/?kbid=823199
-- Tell the senders to remove any reminder before sending you an iCal meeting request.
-- Tell the senders to send to you in native Outlook meeting request (RTF) format, not as iCal.
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Sue Mosher, Outlook MVP
Author of Configuring Microsoft Outlook 2003
and Microsoft Outlook Programming - Jumpstart for
Administrators, Power Users, and Developers