When my friend tries to join my game she waits about 2 minutes on the "Connecting" screen, and after that a message appears saying "Unable to join session. Please try again in a few minutes." or something among those lines. Normally my NAT is strict and i have Double Nat, but i have found a way to make it open and remove the Double Nat, the method has proven to work, because games that didn't work before work now. A weird thing is that some days she can connect normally to my game, but most days she can't. She has tried to join my game in all ways we know its possible(via the Multiplayer>Join, via the Join game option in the Xbox friends panel, via accepting my invite that was sent via the guide icon near the equipments slots, and via accepting my invite that was sent via the invite to play option on the Xbox friends panel. I have read lots of threads on-line but none of them have worked, so i decided to seek help here.