Same issue. Plain in the arse…!

My fix was;
-Try it, lose all hope
-…Cancel and it takes you to dashboard
-Start a game, (this worked for COD/BF3..)
-Sign in when it says you need to connect to Live to play Online
-…should work…

Probably an easier way but this seemed quickest for me today (at least the game was running!)

I did all the SMS and email crap between rounds. Really not worth it. I only have a hotmail account to have an Xbox Live account!