Is that as the "root" (site-wide admin) user, or as the new user?
can you visit <yoursite.com>/register, or does that produce the redirect error above?
If you're getting the message when visiting /register, your permissions are messed up. If it's just for the new user, log in as the site-wide admin and give them 'read' permission on the main site. If it's for the site-wide admin as well, you need the first half of this faq: https://openacs.org/faq/one-faq?faq_id=130897#141496
If you aren't getting the message when you visit /register, it may be a permissions problem with some specific package, or something else entirely. You'll need to provide more information.