For now I would say wait it out. Giving it 30 mins or so might solve your problem. I'm currently looking further into the issue.
Probably the minecraft authentication servers, nothing you can do, but you can look into it all you want to humor yourself
I get this error message sometimes, I just go back to the multiplayer screen and try joining again. If that doesn't work then exit minecraft, reopen it and try again. If that doesn't work then I try again in 10 -15 mins. I not sure why it does this, it could be for several reasons.
Occasionally I will get that too, but then I will talk to other Minecrafters and find that everyone's getting it. It's probably the authentication servers. Are you still getting this problem @2008splash? By the way, how to you tag people with the "@" symbol?