I'm trying to join multiplayer maps and for the past few days i've had graw its been fine but all of a sudden now every map i try to connect to i get kicked out of after about 1 minute and the game says "this session no longer available".

Any tips?

I'd say either bad luck or high ping time.
Any idea if you've been having high pings lately?

I played fine one match for about half an hour with six or seven others (campaign map) and got this same message. And when I tried to reconnect.. yep same message. Not sure about ping times though, how do I check those Catty? I didn't notice ANY lag during game personally.

don't think you can ping a standard xbox360 thru xbox live. you can check your time with your pc thru broadbandreports.com or many other free utility sites.

any of u guys ever get some message that says something like "Arbitration Failed" Not sure if I spelt it right, but i get that ever now and then.

anybody???

That means that your 360 couldn't sync with the host's 360 not the servers. Check the definition of arbitration.