Originally Posted by mskr
I am getting a very similar issue where windows sidebar and outlook are incapable of communicating via any network device except for the GSM (cellular) modem in the PCMCIA slot. It has nothing to do with the routing table or the firewall. There seems to be a layer of Vista that filters TCP at a device dependent level. In twenty (twenty-five?) years of computing and networking, I have to admit I am baffeled. I tried uninstalling all the network devices, but there are two devices (Device Manager) called "Net Firewall Miniport Interface" that (from google'ing) seem to be associated with the AT&T GSM software. They both appear to be corrupted with bad configuration data in the registry, and they refuse to uninstall.
So, this does not fix your problem, I am sure, but check your device manager and see if you have a "bad" interface. It may start to lead you in the correct direction. To the rest of the crowd, anyone got a good way to blow away a device that refuses to uninstall??