Outlook 2003 calendar appointments disappear

[Guest]

here is my scenario

I have 5 users sharing a calendar

Use A adds a meeting to User B's calendar and sents an ivite to user C's
assistant, when User C's assistant accepts the invite, it is added to user
C's calendar and he doesn't need receive any read receipts or invite emails.
It is simply put on his calendar. Also, when E adds something to User B's
calendar it disappears.

We are using exchange 2003, Outlook 2003, and all users have blackberries.

Any help would be appreciated.

charlie