I had this same problem using a Umax Vista S6E scanner with a GVP HC+8 SCSI card and BetaScan in my A4000. The scanner head moved a little bit then stopped when I tried to scan something. I tried updating the ROM of my GVP SCSI card from 3.71 to 4.13 but it made no difference.
I now have a DKB RapidFire SCSI card in my A4000 and it works flawlessly with the scanner.
I'm suspecting the WD SCSI chip common to both the A2091 and GVP boards may be having problems dealing with scanners.
