You can use the Diagnostics tool and view the debug log in ArcGIS License Server Administrator to diagnose errors if client machines are unable to get a license from the license manager or if the license service cannot be started.
- Launch ArcGIS License Server Administrator from Start > Programs > ArcGIS > License Server Administrator.
- Choose Diagnostics in the table of contents.
- Click Diagnose to view the status of the licenses in the window below.
- Click View below the Debug log path to get more error information if you are unable to start the license service.