@Neil

OK I'm sure this is what I did the first time I attempted this, though there was no folder named Garmin in the Garmin labeled D drive in File Explorer.

I followed your instructions as noted and this time I saw the message that it was "loading software", only this time the Garmin folder was created and with in that folder, a folder labeled "GPX" and with that folder was a file labeled "current.gpx"

When the unit begins to boot now, at the bottom of the splash screen it shows:

Nuvi 255W
Copyright 2015
Garmin Ltd. or its subsidiares

that text disappears and "Loading Maps ..." is displayed briefly, followed by,

just the Garmin screen with an image of a PC connecting to a GPS and nothing further.

Not sure if we are any closer with this info or not.

Cheers

Jack