Dantz Development Corporation, the makers of Retrospect (the site licensed
archival/backup software) have found an init conflict between Retrospect and
the Apple Tape Backup 40 SC drive's "Tape Disk" INIT.
Essentially, "Tape Disk" is an init that lets the user mount any tape inserted
into the Apple Tape Backup 40SC drive onto the desktop. However, Retrospect
also has an INIT called "Retro.SCSI" that has been optimized for use with the
Apple Tape Backup 40 SC unit.
Thus, if "Tape Disk" is present in your System Folder and loads at startup,
Retrospect will be unable to recognize the Apple Tape Backup Unit, (even if
Retro.SCSI is not present in your System Folder) whether or not it can be seen
using a diagnostic SCSI utility, such as the "SCSI probe" CDEV.
To fix this problem, remove the "Tape Disk" init from your System Folder and
restart your Macintosh. Retrospect should recognize your Apple Tape Backup 40
SC unit at that point.