So, when my friends go to some server and invite me there, I got something like this: "Game session no longer exists. Returning to singleplayer...", and "Disconnected from server. Returning to singleplayer..." and that kind of messages... I think it's just my xbox/gta because my 2 friends can go to their servers allways they invite each other... Strange... And it is the funny thiing, that I don't know if this is a xbox or gta "bug"... Any1 else got the same messages when some1 invites you somewhere??
edit: Got it, I tested my connection to Xbox LIVE and the NAT said it was Moderate, and now it's Open and this works!