Odd Meeting Request problem

[WhitsellCS]

I've got an odd problem with one of my clients that has BES Express 5.0.1 server on the Exchange 2003 (SBS 2003 Server). We've recently just replaced the BES 4.1 with the BES Express but the problem was occurring in 4.1 as well. I suspect it may be a permissions issue with the BESAdmin account but I'm not sure what to look for. Here's what happens:

If a user in the GAL sends a meeting request to another user in the GAL the meeting immediately gets put on the second user's calendar and marked as tentative, but no meeting request is placed in the inbox. If a user from outside the Exchange GAL sends a meeting request, the meeting request message is correctly displayed on the Blackberry.

The problem is without the meeting request in the inbox the users that rely almost entirely on their blackberries for email and calendar, get surprised by meetings they didn't know they needed to attend until the 15 minute warning beeps at them.

I'm trying to figure out what is occurring here but I'm getting nowhere. I'm hopeful someone here has seen this before.