I'd guess you've made an error in setting up permissions. Specifically, you've revoked 'read' permissions for 'The Public' for the pageroot. Since /register inherits from /, unregistered users get directed to /register, which they don't have permission to read, so they get directed to /register, which.... (you get the idea).
The fix is in the faq: https://openacs.org/faq/one-faq?faq_id=130897#141496
