BB & Hosted Exchange

I'm using a BB9700 and a Hosted Exchange package w/ BES. Every once in a while (including Friday and again today) the BB just won't connect and sync at all. Resending Service Books does nothing, it requires me to deactivate the phone from the Hosted Exchange account, and then re-authorize, including occasionally wiping my phone first.

I'm not a happy camper, and neither my Hosted Exchange provider, RIM, or AT&T has any idea what is happening. Does anyone have any idea what is happening and how to prevent this in the future?