Found the source of the error. If you try to sign up as a new AIM user on the AOL website (URL= aol.com/aim) it will take you to a signup area that fails.
If you click on the “sign up as a new user” link at the initial screen of AIM, it will direct you to a DIFFERENT web page – and there the signup process works fine. So it appears to be a case of poor website redirection on the main AOL site. No wonder Time Warner wants nothing to do with them 🙂
I usually never see the “add new user” link when AIM loads because I auto-login. Disabling the auot-login let me see the option – and there you have it!
Thanks for the help everyone!