I have been using my Dakota 20 with four individual xxx.img-files for a while.
One topomap.img
One streetmap.img
One overlay map with trails.img
One overlay map with cross country skiing tracks.img
All the maps have been saved in the MicroSD-card /Garmin/ folder, and have been showing in the map setup-page on the device.
But now the unit has stopped reading all the "custom-named" xxxx.img-files, and only recognise the standard gmapsupp.img
Does anyone have a solution for this problem?