Having matchmaking/Host Connection Issues

Been having major Matchmaking/Host connection Issues on the east coast at least in my area with any and all friends that have purched the game. For Example...it will connect us to a game then all of a sudden....boom, sorry you suck no game for you....not in those kind words but you get it.....

What error message does it give?
And how are you getting together? Xbox live party or Inviting from the first crossfire menu?
Is the person doing the invites NAT open?

Any specific details can help us a lot to sort out what is going on.