Help with System Link and Wif... Can't see or

I have 2 Xbox 360 consoles and 2 copies of Halo 3 and would like for me and my son to be able to play against each other over my wifi connection. I’ve already created an ad-hoc network, both console can see it, and both get their unique IP addresses from the router. However…

When trying to host a game via System Link from either console, the other console can’t join. Neither console, regardless of which on is doing the hosting, can see the other console game being hosted. And as far as I can tell, both consoles are on the same update. And we all share the same maps.

I’ve wasted about 2 hours trying to figure this out and I’m getting really frustrated. Any help would be appreciated.
Try clearing your system cache and see if it helps. Most of the times that I have had problems with LAN connections this cures it.