Many players booting up Crysis 2 for the first time have found themselves locked out of the multiplayer mode. To play against others, you're required to log in with a MyCrysis account. For a number of people, the system doesn't recognise their log in details, leading many to create new email addresses to get around the problem. It's not just affecting a few players, either. There's already a 47 page thread on the Crysis 2 forums full of players who can't play the game they've paid for.
A separate issue with unrecognised game keys is also causing players trouble. EA have posted a temporary workaround for that problem, and have promised that a patch is incoming. They haven't said anything yet about fixes for the MyCrysis login issue.