I just started to have the same problems. Though I was able to play in the multiplayer area for the last few months, but just a few hours ago I have gotten the same as you have?? Have you resolved your problems?
Also in order to get my multiplayer to work I had to upgrade the game with the two patches from Microsoft. If you haven't done that. then give it a try. Then again, I did, but now I am right back were I started from???