While setting up Forms based authentication I ran into this error:
The server was unable to process the request due to an internal error. For more information about the error, either turn on IncludeExceptionDetailInFaults (either from ServiceBehaviorAttribute or from the configuration behavior) on the server in order to send the exception information back to the client, or turn on tracing as per the Microsoft .NET Framework 3.0 SDK documentation and inspect the server trace logs.
Looking around I came across the following: http://msdn.microsoft.com/en-us/library/ff649234.aspx
Go to your server’s IIS and open Sites | SharePoint Web Services | SercurityTokenServiceApplication.
Open that site’s web.config and add above the serviceMetadata element in the Behavior list.
Now when you login, you should get a more useful error. In my case it was:
You must specify a non-autogenerated machine key to store passwords in the encrypted format. Either specify a different passwordFormat, or change the machineKey configuration to use a non-autogenerated decryption key.
So I added new Machine keys to Admin, 80 and Web Services sites. Then it worked.