When using Backup Exec, it is possible that normal backup jobs to tape run without problems, but when you submit a utility job, i.e. Unlock Library, Inventory, etc., it hangs and then gets queued forever and does not run.
I was using Backup Exec 2010, but I understand this works in previous versions too. If you submit a job to unlock, inventory or any perform any other action on the tape library and the job hangs and never runs despite other backup jobs to tape running fine, you may need to pause and unpause your server.
From the devices tab, you will have a treeview control that lists your tape drive and the server it is connected to. Follow the tree up from the node that represents your tape drive and you will see the node for the server. Right click on that server and choose to pause the server. Then do it again and choose to unpause the server. I did this and the job to unlock the library ran immediately and I also then ran an inventory job that did not hang either.
I am not a Backup Exec guru, and I am sure that there is an explanation as to why this happens, but I do not know what causes it, and since I have a solution whenever that happens, I have chosen not to look into it further. If anyone has information about what causes it, I would love to hear about it.