Hey guys I have some problem with playing BF2 online. When I try to join a session it gives me this message:
"Your CD key is not authorized to play this game."

I don't know what's this about because I played online and it worked last time, but now it won't. I bought the game by the way and I have the CD and everything.

Can anybody help?

You may have been banned by your CD key. Otherwise, you can only try either reinstalling or persisting.