This is what worked for me a couple of months ago, create a Gamespy account if you didn't already, and go to the EA website and get on a chat session with an adviser if Limited doen't work:
I had the same issue and it worked using Gamespy credentials instead of gamesas.com credentials. Then I couldn't get the Limited Edition code to work probably since the game is logged in to Gamespy instead of gamesas.com, but that's another issue.
My GameSpy credentials are identical to my Crysis 2 (gamesas.com ; crysis.com) credentials. Same username. Same email address. Same password.
I *can* login to crysis.com via the website.
I *can* login to the GameSpy client.
I *can* login to Crysis 1 Multiplayer.
I *cannot* login to Crysis 2 Multiplayer.
I don't want to waste my multiplayer serial on a nick my friend's won't recognise. Nor do I want to use a different email address. I don't think there is anything unreasonable about that.
It's high time EA and Crytek got off their arses and fixed this problem. Just look how far it dates back:
http://www.pcgamer.com/2011/03/25/crysis-2-sign-in-problems-lock-players-out-of-the-game/
March 25 2011.
They even promise to issue patches to fix it.
I can't help wondering if they initiated a contract there.
Or at least can be accused of misselling due to a false promise.
They certainly shouldn't be having promotions on this broken game in which so many people can't even use the multiplayer at all. It makes me sick to see them screwing people out of money every time it's on sale.