I had this same problem. I was able to fix it by changing my email address. For some reason the email address I originally used when I signed up killed my account. As soon as I switched it to my back up email everything started working. Then I changed it back to the original email and it wouldn't work again.
I know that sounds weird but all I had to do was change my email.
Thank you MasterPheonix. Changing the e-mail fixed it for me too.
Too bad I can't use the same e-mail that I use for all my gaming stuff, PSN etc, but at least I don't have to use two different Call of Duty accounts.
I even tried my new Call of Duty account with the old e-mail and it did not work after that. It is definitely only the e-mail address that is no longer working with this forum. That is really weird that they can not fix this issue.
I had the same issue, except I didn't use the original account in the forums for long, I thought that was the reason; when I contacted support, they literally told me "yes, your account is screwed, make a new one", and I had to use a different email account.
If the original email you used was the google one, note that that's the one I was using; if you guys had your accounts with a google mail, please notify the issue is specific with google, in an attempt to speed up the one year process of solving account related issues.