You can enter any serial in form of XXXX-XXXX-XXXX-XXXX-XXXX
It only dont work after enter my original serial.

EPIC FAIL

Im also having this issue, just installed it and tried to join some random server, but I get "keycode already in use"

I was having this issue with my retail edition, to begin with I was using lower case with the dashes ( - is a dash!) and was getting the code in use issue. I've tried without dashes and nothing, though using CAPS and dashes I can log onto multiplayer games though I still have to put the code in EVERY time. Guess I'll stick to SP till this is properly fixed.

Oh and Crytek, where is my DX11 patch? It looks fuzzy on extreme which is not cool. (still looking great mind)

Same steam version also i pre ordered this stuff, this is what i get? we will make you level 5 but you are not going to play it..

FIND A SOLUTION CRYTEK

I fixed this problem (as it appears to be a steam problem) by - after putting in my serial code and saving it on the login page within crysis 2 - i closed steam entirely. I then opened the steam folder in my C drive and deleted the 2 .blob files (appstats and clientregistry). I then restarted steam. Deleting the 2 .blob files in the steam folder forces a steam platform update (see how Valve has recommended this solution for many steam issues within the steam forums). Once I did this, I've been able to play for multiple days and dozens of hours with zero "serial code in use" errors. That said, EA has had issues with it's EA ranked servers and so have been user the PCGamer ranked servers until EA fixes theirs. This has nothing to do with the "serial code in use" error but is a second issue I've encountered and how I got around it.

Jessica

one additional note....i also made sure i was logged into the crysis website using my EA login and staying logged in when i played crysis 2 in steam.

Got the same problem and i got the game from the EA downloader

i keep running into issues with this game