Make sure you're using the launcher tool to launch your game before trying to log in. What that tool does is direct you to the Revora servers as opposed to the defunct GameSpy ones.
I noticed I got this same error message when I tried to log into the old GameSpy one, so I'm thinking this may be your problem. If not, make sure you have set the correct C&C:Online password and are using the email you used to register here on GR as opposed to the old one you registered your EA account with.
Also, next time you have a technical difficulty, please report it in the support forum. This forum is only designed for nickname requests.
Thanks!