miniSD need subfolder called Garmin
Ohh... before you start... make a firmware upgrade with the free WebUbdater software from Garmin... the latest Montana-600 firmware is vers. 4.60... expecting a newer version soon...
Now for the maps...
you need to copy the "gmapsupp.img" file in to a subfolder on the miniSD chip called Garmin !
like: E:\Garmin\gmapsupp.img for the Montana to find the map.
If you create a new map via BaseCamp or Mapinstall, this programs will create a subfolder called Garmin automatically and will only use the map name gmapsupp.img
With the Montana you can rename the gmapsupp.img file to any name you like, that way you are able to use several maps on one chip to be able to identify the files with there contains.
Let's say you got the "Garmin City Navigator Europe-2013.30 NT" installed on your PC, and want to send the map to your unit, using Mapinstall, the program creates a gmapsupp.img (will take quite some time to do so regarding it's size of 1.8GB or more) and sending it to the miniSD overwriting any existing gmapsupp.img. Before creating a 2nd map like Garmin City navigator MENA-2013.20 NT for instant you need to rename the 1st gmapsupp.img like Europe-2013_30.img befor you can add more maps like MENA-2013_30.img, Topo-Adria.img and so on...
I got about 15 different maps on a my 16GB miniSD and be able to enable and disable any of this maps individual in the Montana map menu.
Try to enable only the map you are actually using, so the Montana dose not get muddled up in it's memory by several routeing maps of the same area. The older Topo-maps usually are not routing, so they are good as overlay for the newish routing maps without trouble.
Make sure you got the biggest map file on the Montana unit itself... yeah it need to be placed in to the Garmin subfolder too.
a good source of infos regarding the Montana is this web-page: http://garminmontanagpsr.wikispaces....ware%20History