It sounds like you are trying to double-click, or otherwise open, an .img file intended for a Garmin GPS.
You shouldn't do this. Double-clicking tells your computer to "find the program that will understand .img files, and open this with it". But this .img file is not meant for a program on your computer. It's meant for your Garmin GPS unit. Assuming you have an SD card installed in the card socket for your Garmin, simply do this:
When your Garmin reboots, you should now have the OSM map displayed.
answered 25 Apr '11, 21:14
You can create a folder in your garmin device, name it "Map" then copy the "gmapsupp.img" file into it then it should auto load after.
answered 06 Jun '13, 10:02
Seems to have worked for an install of UK and Ireland Maps on My Garmin Nuvi 3597. It did require creating a Map folder, and renaming the .img file
(Didn't work with Map folder in the Garmin folder so put it in general directory).
Thanks very much
answered 23 Aug, 03:46