Where did you store that map on the SD card? I think it needs to be in a folder called Map.
On older Nüvis this folder must be named Garmin. Also, the file must have an .img extension and should be unpacked first.
You can check with Javawa Device Manager if the map is properly installed.
One more thing: many of those country maps share the same tiles (it is not possible to cut the tiles exactly at the borders).
That is the reason for the error messages. You need to select only one map that you need, otherwise it will lead to rendering and routing issues. To prevent this you can combine all those img files to one big map (at least when the total size does not exceed 4 gb) with this tool: http://osm.pleiades.uni-wuppertal.de/openfietsmap/OSM_Combiner/readme.html