ForumAdmin wrote back and suggested that I export my site from my old computer and import it to my new one. He stated that 99% of the time the problem is a typo.
Well, I never did figure out how to export my site -- let alone import it back -- but ForumAdmin was 100% correct. Once I stared long enough and hard enough at my old computer, I found the typo.

Thanks ForumAdmin. You have untied the knots in my stomach.