WORKAROUND
1. Remove tape library from NetVault
2. Restart netvault service
3. Run netvault console and try to add the problematic tape library (NVBU Console -> Device Management -> Add -> Add Library -> in tab "Library selection" double click on the client)- the "NVBU - Working..." window should show up and it should just wait
(at this moment netvault runs in background several processes and waits until these processes finish their work. Two of these processes (svtl processes) don't respond and around 50 minutes later crashes (this can be a reason why netvault is waiting so long).
4. Whilst "NVBU - Working..." window is displayed please run nvpview tool located in <NVBU_install_dir>/bin directory
5. Using nvpview please kill all svtl processes and after that monitor how long "NVBU - Working..." window will wait, if the window after a while disappear it means that the problem is in svtl processes
6. Do the step 5 every time when the "NVBU - Working..." window seems to hang
STATUS
Waiting for fix in a future release of NetVault Backup
