Single Sign On does not work with Forms Based Authentication

SingleSignonException caught.
Exception Code: 0x8062fffc
Source: Microsoft.SharePoint.Portal.SingleSignon
StackTrace: at Microsoft.SharePoint.Portal.SingleSignon.Credentials.SetUserCredentials(String strApplicationName, String strUserAccount, Object[] Args) at MethodName: SetUserCredentials
Message: A call into SPS Single Sign-on failed. The error code returned was '-2140995588'.

 

R.I.P