No luck yet. Here's what I did:

1. Dragged and dropped the 277 KB 082701000620.rgn file onto Updater.exe.
2. Selected the "USB Device" radio button.
3. Brought the GPS unit into pre-boot mode.
4. The moment the GPS unit was recognized by Updater.exe, pressed "OK".
5. Updater tells me the current software version is newer than the update version. Chose "Yes" to replace the current version.
6. Updater updates.
7. Updater tells me the update was successful.
8. GPS unit still flashes the message "SYSTEM SOFTWARE MISSING".

c58k
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c3k4
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lbox

What I did not mention yet but what may be of importance, is that the unit does not first look at software on the microSD. The moment I switch on the unit, immediately it briefly shows the message "SYSTEM SOFTWARE MISSING".