I'm having a problem trying to add an ASP.NET Membership (SQL Provider) user as a site collection administrator in WSS3.
My user can log into the front end website and can manage their profile (modify and save) using my custom forms, so the actual FBA/ASP.NET Membership system seems to be working correctly.
When I browse to the Site Collection Administrators screen (within the site collection, logged in as a different admin user) and enter the name of my user as 'myprovider:myusername', and then click the Check Names button, the user is validated and it appears that the system has recognised it.
However, when I click OK to add the user as an administrator, I get the following error:
The user or group 'myprovider:myusername' is unknown. at Microsoft.SharePoint.Utilities.SPUtility.FilterValidLoginName(String loginName, SPSite site)
Does anyone know why this might be?