Recently I was trying to setup a SharePoint 2010 site with FBA that uses an LDAP provider. I looked up for instructions & I was able to find a tonne of material on how to do this and everyone had given nice snippets of the web.config stuff. But what most (every post that I checked out) people missed was that they need to put in the default role provider within the Secure Token Service's configuration file as well. And this needs to be set to the same thing that you have on the web application that uses the FBA.
