I have an customer where we have the problem, he can't sync any appointments
from his mobile device to his GW PO.

The other way: GW PO -> mobile device works OK.

We tried two different mobile devices: 1. a Motorola Razor 8 cell phone with
GMS and 2. an Black Berry with BES.

In both cases, the appointment sync from mobile device to GW fails.

I guess, there is a problem with the users PO.

Any ideas how to fix this issue?