Many have the problem that they can not log in to the game with their accounts that work well on gamesas.com.

Here is what I found out after trying for hours with many different accounts:

Creating a new account from within the game is what works most reliable.
Do NOT use any preexisting ign/gamespy/whatever accounts.
You can't reuse an old ign login name, but you can reuse your old email address:
1) go to http://www.ign.com/login and - well - login, then change your existing email address e.g. by appending .outdated to it. It doesn't have to be a real email address - check if out - you will still be able to log in to ign.com with that changed address.
2) now your original email is free again. Use it and a *new* login name in the game client to create your crisis2 account
3) you should be able to use this account in game and on mycrisis.com
4) Only if you checked ok to login on game and mycrisis enter any serial codes for multiplayer or to get your promo items.

Best of luck to you all.

I don't see where i can change email on ign. Only verification.

Login at ign.com, mouse over your nickname and select manage account.
After that page is loaded click Button 'Update Profile'.
There you will see your user data including email. You can directly change it. Then enter account password and select button 'Save and Finish'.

After i clicked this button my brouser tries to download unknown file. NoScript disabled

Interesting, well i tried to follow this guide of yours but when i log in to ign.com it doesnt have this nickname at all :O.
It shows on gamespy.com and gamesas tho. IGN seems to be using my old old old old temporary nickname i had to use looong time ago.

Hmm, I just checked with Firefox 3 and 4 and IE 8. Worked every time. The page is very slow, but eventually finishes for me...

I had several nicknames registered with same email address. Also my old gamespy nicknames were there. I gave them all different email addresses to separate them again.
As gamespy and ign accounts should be essentially the same it is very strange that you cannot see your nickname in ign but see it on gamespy. You sure to have used the right email to log in?

But sure, strange things happen at this ign account management. Strange decision from crytec to use this buggy thing for the release of their game. Also this issue was also happening in beta.

Alright, i was able to create "new" Crysis 2 ingame account with the same email im using here.
I created the new ingame account with my gamespy unique nickname wich is this "Ekido" but nickname i cant login ingame is "Azze"
The problem definetly is with old gamesas accounts, the old account data havent been transfered to Crysis 2 systems or something i don know :l