Red X when trying to accept meeting invites

[rowlans]

I have one BB 8900 out of 200+ that intermittently show a red x at various times when trying to accept a meeting invitation from a colleague. We run a BB server version 4.1 & exchange sp2 with multiple devices running...BB8320, 8310, etc. Only this one device is doing this and so far, no one has been able to help...not T-Mobile, our IS department or BlackBerry. Anyone?

reregister them, on the servers....resend Sb's.........