I have no idea what the fault is either and I am an expert at these things. The machine is running just vanilla Windows 7 64 bit entirely up to date and it runs faultlessly with everything else I throw at it. It no longer matters to me though, since I did what I had to with the wallet for now. I will probably just run up the wallet daily from now on to keep it synced. I will definitely try it on a few other machines though, just to satisfy my curiosity.

Thanks for all your replies