are the users syncing with handheld devices? that is the most likely cause.
If using a Blackberry, they should not do anything except view appointments-
accept, decline and delete from them outlook. (It may be true for other
devices too - I just know blackberry. )

--
Diane Poremsky [MVP - Outlook]
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"Newbie" wrote in message
...
I have had a number of complains where users didn't receive the invitation
or meetings being dropped from their calendar and they missed the meeting.

How can I trace from the system to find out what happened?

Our server is Ex2007 SP1, clients are running Outlook 2003 SP3.

Thanks