Found a solution for Crysis 2 MP...!!!
Well guys just like you I was hoping to play C2 MP after the deactivation of the "serial code" and I didn't stop to search for solutions... Then I came across a website and there was a post about C2 MP... It said:
If you wanna play mp, then when you start the game, login with a random code and before you run to click on multiplayer, unplug the connection between the computer and the modem. It will say check your connectivity or something... (and should return to the main screen and not the login page...)then, replug the connection and walla... your in. Believe me I was playing for a long time tonight before I lost connection with that server...
Thank me if it works for you...