I've added the membership and role provider keys for  an FBA database into the web.config of a standard AD authenticated  SharePoint site (as per Andrew Connells article).
  This should then allow me to add roles and user to the site that can  then be subsequently used to log in via an FBA configured Url.
  When I add in a Role or User it should become underlined in the  people picker dialog of the add user page, to show that the role/user  has been recognised. 
  However this is the problem, I cannot get the roles or users to  resolve and 'underline'. I have other sites configured in exactly the  same way and working correctly, I just can't seem to get this site or  any newly created sites to work as expected.
  I've checked and rechecked my web.config entries, I've even pasted  the entire web.config file from a site that works correctly into a  problem site but I still can't get the user or role to resolve.