Bf2 - invalid serial

(Really? No such product as Battlefield 2... really?!!)

First of all, I spend 3 hours looking on the net (including this web) for some kind of actual support and this is the closest I could find.
I bought the complete collection (battlefield 2) from steam and played it for a few hours. After that I wanted to try the special forces which didnt work and said that my cdkey is invalid. I did some search and found a solution in steam forums. Of course it didnt work. Not only it didnt work but it made the message appear in normal bf2 too. I reinstalled both the game and steam, deleted all registery keys but still - key is invalid. Tried going to the support folder and entering it manually but again - the same error.
I think that the cdkey got somehow blocked, what do I do?