most likely the insert record behavior on the registration page is set to redirect to a page that you have security assist access applied to, I would need a copy of the registration page and the page it redirects to in order to validate that though.
Your friends over here at WebAssist! These Dreamweaver extensions will assist you in building unlimited, custom websites.
These out-of-the-box solutions provide you proven, tested applications that can be up and running now. Build a store, a gallery, or a web-based email solution.