The library server was unable to contact the library client for the given interval to verify that the library client is still using the drive. At this point the error recovery logic of the library manager will reclaim the drive (including dismounting the client's volume if possible) and allow other to use the drive.
None.
Verify that the library client with the above server name is still running. Verify that the sessions have not been disabled and the network is still working between the two host machines. Verify that the server definition (QUERY SERVER) on both the library manger and the library client are correct.