Battlefield 2 "Invalid CD Key"?

I have an old copy of battlefield 2 for pc. it works on my computer and i have the patches both 1.41 and 1.5. I can play single player and retrieve my old account. But when i update server list and try to join a server it says "CD key is invalid". I have tried reinstalling the game, Changing CD Key in files, and a few other things. Any other ideas? I lost the manual so i just got a CD key online from some site but it works. Please i really want to play.Battlefield 2 "Invalid CD Key"?
Oh yeah, the problem with BF2 CD-Keys. Many people who bought it on steam (including me) couldn't go online. It was because every time you went into BF2 the registry would reset the CD-Key. On Steam BF2 forums someone had made a fix, that after BF2 launches the fix would automaticly enter the CD-Key...Search it on steam forums, it should be stickied, if not, just browse a few pages.

Edit: http://forums.steampowered.com/forums/showthread.php?t=1680864

Here is a link to the fix. Might not work the first time, but keep trying.