Sync Errors with code 0x85010005

I have a sync error when sync-ing with an Exchange server. When I connect my
device to my PC via USB, I get the following errors in WMDC; "The server
could not be reached. This can be caused by temporary network conditions."
The Error status code is 0x85010005.

I believe this is a 404 HTTP error, and caused by the fact that I have
external domain, (mydomain.com), and internal domain, (mydomain.local). I
have already configured my device to sync with my Exchange server over GPRS,
which it does, no problem. I'm guessing the error is to the fact that the
configurations settings have the external address of the server, and cannot
resolve the Exchange server internally.

Anyone know of a work around?

Exchange 2003 (SP2)
Windows Vista 64x
HTC Touch Pro (WM 6.1)
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Al