Debugging umass

Hi All,
Can anyone give me some tips to get a USB Flash disk to work? I've been mucking 'round all morning fiddling with flags in umass_quirks.c trying different options, but can't find a combination that works. Device is a Seitec USB Bar - uses a Prolific PL-2515 chip (PL-2517 storage). With BBB I get:
umass_scsi_cb: status cmd failed for scsi op 0x25 sd0(umass0:1:0): Check Condition on opcode 0x25

    SENSE KEY: Not Ready
     ASC/ASCQ: Medium Not Present
sd0(umass0:1:0): could not get size
sd0: 0MB, 0 cyl, 64 head, 32 sec, 512 bytes/sec, 0 sec total With CBI or CBI_I I was getting a lot of timeouts. I've tried NOMODESENSE, and NOBIGMODESENSE, but to no avail.

-- 
Craig