I've noticed that my GSII won't connect to the MS Exchange server when I'm connected ove WiFi. Any idea why? I have no problem syncing to Google or anything else. The WiFi network is protected and is located at my work office.
It has to do with your activesync needing to connect to the external (public IP) interface of the Exchange server, and your firewall or some other condition is preventing that from the inside of the business network.
EDIT: Figured mine out, go to the above thread to see what I had to do...