Need help, can't join games

[Robotic Pope]

Sounds like a Strict or moderate NAT problem. One or more people already in the lobby can't connect to you so you can't get in. If you are using a router make sure the right ports are open ( by manualy setting them open or putting 360 in the dmz or activate PnP)

[mattd27]

Maybe, but here have actually been times when I've failed to get in a room through the invite, then found the room in custom match and been able to join. Nevertheless, I'll try what you said, and see if it makes any difference.