I used to always have problems connecting to other people on Halo. I could connect fine to Matchmaking games by myself, but I very rarely could join Tom or anyone else on Adelphia. If either of us tried to connect to the other person’s party, we’d see the same error message:
You aren’t able to join this party because we’re having network problems. Sorry about that.
I used to see that phrase in my nightmares. Microsoft even has a KB article on it. Last week, through my endless scouring of the net, I finally found the solution. I’d give credit where credit is due, but I can’t find the forum posting that I found this on (if I do, I’ll add it here), but here is the simple quick solution:
Turn off UPnP on your router.
That’s it. For my Linksys WRT54G router, UPnP is on the Administration tab, and since I turned it off, I have been able to connect without any problems. In case you’re curious UPnP is “used by certain programs to automatically open ports for communication.” (According to my router’s help). I haven’t had any problems with anything since I set it up, so I would say it isn’t too important.
Edit (06-26-06): After I moved, the problems came back. Making my XBox the DMZ host and turning off UPnP seems to have worked…for now.Edit (11-03-07): I no longer care about this. Halo 3 fixed whatever the issue was, and I doubt I'll be playing much Halo 2 on Live anymore :)