Thanks for the reply. I forgot to mention that the Cisco is not doing NAT, and that my machine has a real-world routable IP address. I also tried it on my home PC which is the same setup, but is behind a Cisco 1700 series router, which has minimal configuration and no NAT. The only routing in it is interface Serial0, ip unnumbered FastEthernet0. My home PC also has a routable IP of 38.116.129.243, but experiences the same problem.

At home I disabled the Vista firewall and AVG (which doesn't have a firewall anyway) but the firewall icon still shows up, is that normal?