Tape library shows offline while the tape drives show online. The contents of the Slots may or may not be visable. If Library is removed and readded 2 librarys appear as connected to the NVBU server despite Windows Device Manager only showing 1.
Library had previously been removed and then added back with a different name. The old name still existed in a Target Set.
To resolve this either Delete the old Target Set or Edit it to point to a different device. Once that is done be sure the old library and the re-added library are removed from Manage Devices. From the NetVault Configurator Stop the NetVault service. You should now only be presented with only 1 library and once configured should show as online.