Both good points, Jerry & Rafael. Thanks for taking the time.
I realized that I left out key pieces of information on my first post: The flash cards are recognized by both the Finder AND by FCP. That is to say, the card mounts on the desktop and I can access the files in Finder. Also, although Log & Transfer “sees” the card, it can’t access the files because, according to an on-screen notice, the file structure on the card is the problem. This happens only on the Octocore; not the two MacBook Pros, where L & T accessed the files just fine.
I have tried with three different flash cards and had the same result with all three. I also copied the entire contents of one card to an external drive and tried to access the files that way but, once again, Log & Transfer on the Octocore said the file structure prevented it from proceeding.
Once again, thanks for your time on this.