out of date

We have 50 users in our firm. Out of those 50, one person had this issue:

A meeting invitation was sent out to quite a few users and only on his
Infobar it stated that the message was Out of Date. (This problem happened
last Thursday and then again Monday, but not any other time)

He is a MAC user and accesses mail through MAC Mail, but uses the terminal
server to access calendar appointments, contacts, etc. If aother user is on
the Terminal Server (which has Outlook 2003, sp3 installed) and sends an
appointment to this person, there is no issue and the appointment date/time
is correct. However, if a user sends an appointment from their own desktop
(also Outlook 2003, sp3) to him, all the appointments will show that they are
"Out of Date". Again, only on 2 days. The rest of the time it is correct.

He did not accept the appointments via his iPhone nor does he access them
through MAC Mail.

These meeting requests were original requests. They were not updates, they
were not cancellations. Some were all day events. They were scheduled for
several different days.

As a result of accepting or declining the appointment based on that
information, his calendar could be incorrect.

Thanks for your help.