So, my friend and I have been playing Sins for a while now, using a crossover cable between our two laptops (my Mac running Windows XP SP3, and his Acer running Vista), and it worked for a long time.  For some reason, he could never host games, as I always got an error telling me I was "Disconnected from Game Server", so I always hosted.  But recently, it became more and more frequent that he got the same error, and was forced to restart his computer before working.  Then, it would never work at all, even with restarting.  And now we can't even see each other's games.

It's not a firewall issue; we forwarded the right ports, and eventually, took down our firewalls.  Does anyone know what the problem could be?