After the new patch, I can't get into multiplayer. It tells me my serial is invalid--but it had better be valid, because it worked before and I bought the game on Steam.

yeah same here
I played today without a problem, now i can't play MP
crytek STILL sux :/

Same here....messaged CRY TOM too.... This is starting to ...no wait it iIS VERY **** ANNOYING......can I have my money back? Will they ever (They being any game company) develop a bug free game?

Most of us get this error, it's no help..