depending on your library - if you are having issues:
Some robots will not allow you to load a duplicate tape VOLSER - found this out when I removed a tape stuck in a drive. The robot thought it was already inside, would not allow reload. I had to audit and run inventory, so it discovered it was not there, then I could load it.
Some robots will not allow you to load a tape upside down. It will read the barcode, but not load it.