Well, I tried it one more time, removing the SD card (as some suggest) before copying yet another copy of the update file to the root directory of the Nook. It continued to ignore it, as earlier. So I took your advice, lightcap, and rebooted the Nook. That did the trick - after it finished rebooting and then started up normally, it went to sleep as normal and then in about 1 minute it started the update.
So, rebooting seems to be the answer on systems that are ignoring the update file. Yes!
