Fixed!

I took out the newly installed RTC (Lithium) battery, turned the unit on, and the unit reported January 1, 2000 as the date. And it let me set today's date. Of course, when I turned it off, the unit forgot the date because the RTC battery wasn't there.

So I reinserted the RTC battery, turned the unit on, it reported January 1, 2000 as the date, and it let me set today's date. And when I turned it off, it remembered the date.

Problem solved--without a firmware update, too.

My Argo-Navis hasn't been used since last autumn, and the batteries ran down. I replaced the little lithium battery and the AA batteries, and when I went to set up the date and time, the unit reports November 29, 1999 as the date and won't let me change to July 17, 2020.

Any ideas on how to fix this? Perhaps a firmware update?