"CMOS checksum error" and upgrading the BIOS

My OpenBrick will no longer cold boot without displaying the message
"CMOS checksum error - Defaults loaded" and waiting for a keystroke. 
This is highly annoying because I'm running it without a head/keyboard,
so if my power goes off momentarily I have to find a monitor and a
keyboard just to get this thing to reboot itself.

How do I fix this problem?  I tried clearing the CMOS via the jumper but
that didn't help.  I notice someone else on the list has the same
problem but I didn't see a reply to his question.

I thought maybe upgrading or reflashing the BIOS might help, but I can't
figure out how to do that.  How do I do that?  I'm running off a
CompactFlash card and don't have a hard disk.  I tried installing
FreeDOS on a CF but couldn't figure out how.  Copying the floppy and ISO
images to a CF don't work.  I tried formatting a CF card from DOSEmu in
Linux, but couldn't get that to work.  I tried burning a CD with the
FreeDOS ISO, and booting that from a USB CD-ROM drive on the OpenBrick,
but the OpenBrick ignores my USB CD-ROM drive (even though the BIOS was
set to boot from USB-CD first).

Once you've explained to me how to flash the BIOS, which one do I use? 
There are three BIOS files on the web site, in no particular order.

Fred