Genius that I am, I have figured this out. The CD disk burned with the files must be "finalized" -- i.e., closed with no additional writing permitted. That seemed to be the trick. I was using a disk that was still open.
Why does he want to do this? someone might ask ... well, I can transfer about 700 megabytes of files from my trusty computer to my 9000 hard disk from that single CD, anytime, and not have to use umpteen hundred slow floppies. Or use "direct disk" load from the CD, etc. etc. after I fill the hard disk. It works, well. I just never took the time to puzzle it out and get the necessary CDROM drive, cable, enclosure, etc. before.
Thanks to anyone taking the time to even think about this on this older PSR unit.