This error can occur if the Enterprise Server has previously run the setup wizard, but is now encountering problems connecting to the database. This could occur after you have restarted the machine running the Enterprise Server and the SQL server is taking a long time to restart, or it could indicate general database problems that are preventing the Enterprise Server making a connection.
If you click OK this will allow the Enterprise Server to retry the connection to the database and then you can re-attempt the login.
If problems persist however, to investigate the issue further you should first open the event viewer on the local machine.
Run the command "eventvwr.msc", or open the Event Viewer from the control panel.
Navigate to the DESlock+ section. Find any Error events with the Event ID 259, and the source of dlpecsrv. The event description will contain the actual error generated by the SQL native client and should be used in diagnosis and resolution of the problem.