After configuring FBA for an extranet site. I always get “Unknownerror” when I try to sing in. the steps followed are described here :
1- check for the application poolidentity that host the extranet site.
2- Goto SQL Server to your FBAdatabase created
3- Give put the app pool identityaccount in dbo role. Make sure to put there. It is not enough to map it to dboschema as a default schema
You can detect this error in MOSS logs under : C:\ProgramFiles\Common Files\Microsoft Shared\web server extensions\12\LOGS