Hello again, Bart!

I went back through your article carefully and found the missing piece. I flipped the switch on the lens from AF to M. Evidently, while the image appeared to be in focus, the AF function needs enough light to determine if the flash is needed or not (as you cannot disable the flash in P, S, A or M through the menu.) Only after flipping this would the camera fire, even though the display still stated that the "Subject is too dark".

Thanks again for the post!
Cheers!
Robert