I've had this problem before. It's because you haven't confirmed your email to the site. After a few days, or weeks, of not activating your email to the forums, the server won't recognize the account and will disable the account to be used. At least, that's what I could figure out during my years of FeralHeart. There's a slight possibility I might be wrong, but I doubt that I am.
Always make sure you activate your email before you create an account.
Make sure you activate your account through your email.
Also, always double check all the details through your profile on the site.
An account doesn't just magically disappear unless there's something you forgot.
I recall Starrk's issue myself and I remember how clueless we were until he figured it out.
I suggest waiting until the registration is back open again, I'm not sure what else could be done.