Update. I downloaded V.27 software on a Mac and burned to CD with Toast. It created a disk but still no luck getting it to load in the MK III. Not sure which mode it was (mode 1 or 2). I think I will try again to download using a PC and imgburn. Also, I came across this post and wondered if this applies in my case. If so I am really lost:

NAVIGATION COMPUTER REPLACEMENT - MK III AND DVD NAV
When replacing a defective MK III or DVD NAV computer, a configuration signal is required to allow the new computer to load the correct software for its respective application. This is generated by using the SSS (Software Service Station) loaded with the latest Progman version, and the navigation system operating software CD V17.1 or V32.

1. Connect the Deutronic battery charger to the vehicle.
2. Connect the SSS via a diagnostic head or an O(P)PS (for D-CAN vehicles) to the vehicle.
3. Open a "New session" in Progman; select "Load SW" and follow the on-screen messages.
4. Select "Retrofits".
5. Select "Languages".
6. First select "Display" to select and/or check the correct languages.
7. Then select "Navigation" to select the languages for the NAV system.
8. At the prompt "Is the CD-ROM present?" select "Yes", but do not insert the navigation CD into the Nav Computer yet!
9. First select the main language and then an additional language (the choices are English, French, Italian, Spanish, and German).
10. NOTE: The gender of the announcer's voice (male or female) can no longer be selected.
    • MK I, MK II & MK III: Only male.
    • DVD-Top NAV, NAVI01, NAVI02 and NAVI03: Only female.
11. After activation of the automatic coding, the DIS tester tells you to follow the instructions on the monitor for navigation CD installation.
12. Place the navigation CD into the navigation computer CD drive.

Thanks in advance for any help anyone can provide on this.