It seems that this slave tried to restart itself, but never started up properly:
2013-08-21 16:57:22: Scheduler Thread - Seconds before next job scan: 2
2013-08-21 16:57:23: Scheduler Thread - Current task complete, restarting slave…
2013-08-21 16:57:23: Slave - slave shutdown: normal
2013-08-21 16:57:23: Slave - slave shutdown: normal
2013-08-21 16:57:23: Warning: can not call Slave.Shutdown() when Slave.Mode is ShuttingDown
2013-08-21 16:57:23: Listener Thread - OnConnect: Listener Socket has been closed.
2013-08-21 16:57:23: Info Thread - requesting slave info thread quit.
2013-08-21 16:57:23: Scheduler - Returning all limit stubs.
2013-08-21 16:57:23: Scheduler - returning nuke
2013-08-21 16:57:23: Scheduler - returning 521551b3af37900e7411516c
2013-08-21 16:57:23: Info Thread - shutdown complete
2013-08-21 16:57:23: Scheduler Thread - shutdown complete
The slave was not running on the machine