Brad,
Thanks for your reply. I've actually gotten more clues since I posted this issue, although I have not yet resolved it.
I ran TAP on another machine and built a basic image for it and copied the image to the same USB thumb drive in question. The system boots to the thumb drive flawlessly. FBA ran, everything was good. I then put the USB drive into the original target machine, and it booted fine (although it didn't have the correct drivers).
SO......I'm wondering if it's a FBA thing...or what. When I re-created a new image for the troubled target machine, I got the same thing.
Strange.