So a friend and I bought Sins, and we're trying to get an online game going. We can connect to ICO fine, but every time we try to join one another's game we get a long pause followed by a "Disconnected from host" error.

What we've tried so far:
- 6112 is open on both systems, on UDP and TCP
- UPNP is up, as are both XP services required, on both machines
- Neither of us has windows firewall up.

Any thoughts?

EDIT:
He's on Vista; I'm on XP. We can both connect to other games.