So I boot up crysis 2 this morning because it has been a while since I have played it only to get a message saying my serial code is invalid. Everything has been perfect till now. How the hell is it invalid if i've been using it to play all along? I tried re-entering it multiple times and always get the same error. Is anybody here suffering from the same problem or know of a potential fix? I would really appreciate it, thanks.

Check your serial code inside "EA Manager". My code happened to have the "7" exchanged for a "Z". I changed it inside game lobby and it started to work properly.