This is strange.

Assuming that barcodes can be detected i can only think of two possibilities:
  - You are also using an incompatible barcode format
  - The barcodes are upside down.

Let me suggest you run "sjirdtag scsidev@<your_jukebox_scsi_address>" to verify 
what the jukebox sees and whether the slots are really show up as loaded.

Another potential problem could be a bad cable and/or terminating issue which 
lead to intermittent problems.

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