You didn't state what the OS-type or version is, but, when nothing is running, at the comand prompt, see if there is a hung session
omnistat
If you see any, use the session ID to try and kill the session
omniabort -session [session id] Do not include the [ ] marks
Stop Data Protector, and check to see if there are any running sessions
UNIX Cell Manager
ps -ef | grep omni
Windows
Open Task Manager, get a list fo running processes
Look for any 'xSM' (for example BSM, RSM, MSM, CSM, ASM) processes, if you see any, then kill them
Start Data Protector, and run
omnidbutil -clear
omnidbutil -show_locked_devs
If there are any locked devices or cartridges
omnidbutil -free_locked_devs
omnidbutil -show_locked_devs
This should free up your device. If not, the Media Agent should probably be rebooted, because teh device is locked at the OS-level