This has been happening to me and my mates the last week or so too: very frustrating!!
Sometimes if you restart your Xbox you can sign into the servers, if not trying playing an offline game then signing in after you have completed this game. If you still haven't got on after this it might be worth playing something else and trying it again later?!!
...by the way I don't think EA are to bothered with this problem though due to the fact that FIFA 12 is upon us at the end of the month!