Did you set your own MembershipProvider and RoleProvider as default providers? Currently you need to do this, because there is an issue in the current RC of Sitefinity, which didn't allow the use membership and role providers for Cms Users, which are not set as a default .
Otherwise, you should set the name of the providers for Cms users in the web.config in the cmsProvidersName attribute value:
<security defaultProvider="DefaultSecurityProvider" cmsProvidersName="Sitefinity">
<add name="Administrators" permission="Unrestricted"/>
<add name="PublicUsers" permission="None"/>
In this context the Membership and Role providers for the Cms Users should have the same name.
You don't need to implement anything. If you are still having problems, please send us your web.config and we will check it for you.