>The library is a Sun L3500, the drives encounter the errors when it tries to
>mount a tape for processes such as reclamation or migration.  There is no
>tape stuck in the drive, I checked all SCSI connections and cleaned the
>drives.

Long - It sounds, then, like the library believes that the drive/slot is
       occupied, as though something irregular recently happened in the
library.  If the library supports a "reinventory" operation, try that to
see if it will cause the library to reacquaint itself with the reality of
what's occupied and what isn't.

  Richard Sims, BU