The user should not be restricted from logging in once they are registered and confirmed. It looks like the page just refreshes when the user clicks on the login button? Is there any error message present? What is in the address bar when this happens? Do you see any accesscheck variables with page names present?
Please post back with this info and a copy of the login page, or let me know if it is the default version of this page. If there is no access check in the address bar then the authenticate user server behavior may not be getting triggered properly. I have seen issues with certain triggers before on various servers, for example the http_referrer is not always set the same for every server so the check for this could be not passing. I have no idea if this is what you are experiencing but if you can post back with any additional details it will help.
