There is no such thing as MS 2000 and MS2003. I presume you mean Outlook
2000 and OUtlook 2003. Microsoft offers a hotfix for Outlook 2000 to improve
its compatibility with iCal/vCal 2.0 meeting requests. See
http://support.microsoft.com/?kbid=823199 . Alternatively, have Outlook
2002/2003 senders avoid using reminders in the meeting requests they send to
Outlook 2000 recipients.

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Sue Mosher, Outlook MVP
Author of
Microsoft Outlook Programming - Jumpstart for
Administrators, Power Users, and Developers
http://www.outlookcode.com/jumpstart.aspx
> Trying to send an calendar appointment to another user of MS 2000 from my
> MS
> 2003. It arrives encrypted instead of an appointment. How can we fix this?