Garmin Montana 600 Can't unlock maps

Hello all

First post so please be patient :classic:

I've had a good read through a lot of information on this site. Some really great tips and useful info, grateful for that.
:classic:

I have a Montana 600 with software 5.20. And I have loaded Basecamp 4.6.2 onto my laptop, which uses windows 10.
My Montana is second hand and came with the following maps.
CN Europe NT 2015.20 V 2.00
Garmin Discoverer GB 50k all V2.00
TGBD038 GB National Parks 1:50 V2.00
Garmin Coast to Coast.

I want to put CN Europe and Discover onto 1 SD card so that I can use each map with a different profile ie Discoverer for trailriding and CN Europe for the road trips.

I have down loaded the jetmouse unlocker with the fix.
I have worked out how to get the SD card serial no.
And found the map ID (except for the coast to coast map)

I have managed to copy the CN Europe and Discover maps onto the micro SD card.
I can see both maps through Base camp, however. When I put the card into the Montana I get the
Can't unlock maps message.
Checking the map file in the Montana I can see the CN Europe map is enabled but no sign of the Discover.
I've also copied the National Parks map, that is the same as the Discoverer. IE I can see the map in Basecamp but not in the Montana.
Checking the Garmin folder for each map I found that only the GB Discoverer map has a GMA file.

Not sure why the maps don't unlock in the Montana.

Can anyone point me in the right direction?
Thanks:)