Chris,
By default, the 9330 code does not allow "J Carts" (in other words, IBM 3590 cartridges), to exist in a 9310 library. At install you have to specify that 3590's are attached and obtain a suitable number for the SME environment. This action was known within STK as "J-Cart recognition feature" and was a measure put in place to stop IBM willy-nilly swopping out 4490/9490's for these own (superior) drives. You cannot later visually verify if this feature is on or off.
If the probelem is elsewhere then its a cracking problem. My second guess would be the backup application not processing the 7th digit of the barcode correctly, but if that was the case then you would expect to see ACSLS (which sits between the LMU and backup application) giving no errors. I would check this by doing an ACSLS query of known 3590 volsers in LSM1 and see if ACSLS shows them correctly as IBM 3590 media or unknown.
STKman