Anyone seen this scsi error before ?

[Graham Bentley]

Recently swapped out my Sony for a HP DAT and
got this first time in dmesg

(sa0:ahc0:0:6:0): PREVENT ALLOW MEDIUM REMOVAL. CDB: 1e 0 0 0 0 0 
(sa0:ahc0:0:6:0): CAM Status: SCSI Status Error
(sa0:ahc0:0:6:0): SCSI Status: Check Condition
(sa0:ahc0:0:6:0): UNIT ATTENTION asc:28,0
(sa0:ahc0:0:6:0): Not ready to ready change, medium may have changed
(sa0:ahc0:0:6:0): Unretryable error

Anyone shed any light upon it ?