We are having a tape library of ATL quantum P2000 which is having 4 tape drives.
In which we used to daily backup.
When ever we are keeping any new cartridges into the library we will run an inventory , During this time if their is any kind of cartridge in the tape drive their wont be any issue with that particular tape drive .
If not it is showing a problem of NO BAR CODE on the operator panel of the library.
and at this time it is not detecting on the legato software also.
Your description suggests there is a broken barcode reader inside the library.
Broken parts cannot be fixed by a discussion on a forum.
You need to contact whoever you use for repair services and get the library serviced.