New User Registration Not Working With Pro Sites

I have a problem registering new users. I have set up the registration page on my site to be http://www.pharrac.com/wp-signup.php . However, on activating Prosites plugin, I am redirected to http://pharrac.com/pro-site/?action=new_blog and there is a message "You must first login before you can choose a site to upgrade:". How do I enable user registration with Pro Sites working.