Hey, I know Yahoo Doesn't have a 1-800 number for free mail usres, but I do know of a more direct e-mail address that will go to the technical dept. I understand you are not a mail plus user, but give this a try, this should work, this e-mail is for the free users, [email]mail@yahoo-inc.com[/email]. Of course temporarily you might have to open a different Yahoo ID incase there might have been a bug or something detected in the one you have. Just make sure to include your Yahoo ID, Date of Birth, Zip Code and Alternate e-mail address to prove you're the person who created the account, then Yahoo can check things out and fix it for you.

You might also want to include what internet connection you have, wireless, dsl, etc. what browser you use, if you've deleted your temp files and cookies and if you've used any other browsers or computer and still get the same message.

Good luck