[andrews]

Well...

I had exactly the same problem. It ended up I got a virus/trojan from somewhere and it was messing with my internet connection. Seems that Activesync needs to connect to to the internet to work (or at least you can't have a "bad" connection). Because this was my work laptop, I reformatted and reinstalled AS and my phone worked again.

So my guess is something is wrong with your PC, not your phone.