And thats is the root source of your problem. If I read you post right at this time you do use 2 accounts.
1. The one that allows you to play the game, which is based on your former crysis1 account that also is properly linked with a gamespy account.
2. The one that allows you to post in the forum, but for a reason never really got linked with a gamespy account.
The reason why you can't use account 1. for mycrisis is that it never got registered for the gamesas site itself. And never could be, cause in case you would give it a try with the same username, email and password you used to create your crysis1/gamespy combi account it would tell you that the account is not available, cause it fails to register the account at gamespy cause you already got the account over there.
The reason why you can't use account 2 for the game is prolly that it never was properly synced with gamespy at all or didn't create a gamespy account as it should have done by the time you registered it.
What this fix here might do is it allows users that have a registered mycrisis account that is also linked to a gamespy account already to change their username, cause by the time the account has been registered there was no check if the username would even been available as a gamespy username as well, so they prolly just got a username that is already in use by another gamespy user. And in case the gamesas account never got registered at gamespy it just tries to do so. But thats just a guess and it would be the best if some of the mods would take time to give a feedback for what invalid account info states the fix was meant to be.
The only way for you and many others would be to create a totally new account from the scratch by using the Crysis 2 game account creation screen. Which would need you to use a totally different email adress than you have been used before to either create an account for mycrisis or any gamespy account you might already have. Now that the account creation properly checks if email as well as the prefered username is available on both ends mycrisis as well as gamespy it would properly register an account for both, as it was meant to be from the very first begining, just never really worked. But this would only be an option for those that didn't redeem their LE code yet.