[DavidinCT]

Could be a few things, I would start by checking your account, your account could be denied mobile sync access (just a small check box in your account settings on the server 2003/2007). This could be possable it got checked or unchecked by mistake.

If your Exchange server has a valid certicate, it should sync but, in some cases, I had to export the certificate and install it as a trusted domain to the PPC....(this tends to be needed on custom or beta roms, never had an issue with the factory installed rom)