Quote Originally Posted by any06 View Post
There is a *.gma in /.system
After backup, deleted. Startup message changed to cannot authenticate map, still not appearing in MyMap
I suspect the *.gma file is related to another map on your device, not the CNE NT 2015.20 map you're trying now. After all, there is a Lifetime Mapupdate subscription linked to your nüvi 50LM. If that is the European map, there's no need to get any unlocked UK map working on the device. Further, your nüvi 50LM would need the NTU version of the European map, not the NT version. JCV for instance would not work.

Basically, if the downloaded unlocked UK map works fine on the nüvi 765, it should be recognised on the nüvi 50LM too.