Jim, thanks for that, particularly your BTW. No, I was using an Apple wireless board. As soon as I switched to a wired board there was no problem. Now what I would like to know is why, Oh Why, can't one do a safe boot with a wireless board?
Because the drivers for the wireless keyboard do not load until after the computer starts booting.
You might have better success if you keep holding down the Shift key until the screen changes to blue and you see the startup screen, but it may be that you can't do this with a wireless keyboard at all.