Make sure that you have Reselection option set same way for all scsi devices. Preferably reselection switched on for all. I had once reselection disabled for some devices and got scsi-bus lockups then. Check it with Unitcontrol program from scsi-tools archive for example. Then you can set that option with ScsiConfig program for HD:s and with MyUnitcontrol (from aminet, add to user-startup) for CD-roms.
