God damn it!

This has been happening a lot to me and always will happen! I've been having a lot of trouble with Multiplayer invitations on GTA IV and it's DLC. e.g. when I receive an invitation from a friend and I accept it and wait for the loading screen to go by, a message will come up saying that the session no longer exists. No matter how many times my friend sends the invitation. Another problem is that when I want to send an invitation to a friend, like usual I go into my phone > friends, and it shows the list of friends. But  sometimes when a friend IS playing, the IV logo is not next to his/her username. It will also say that he/she is offline even when he/she is not. Is there any reason for this to happen? I really need to know why! Does this happen to anyone else?