Regarding to your post here:
You have set the build option of your "map.tmx" file to "copy", but this will just copy the file (untouched) to the output directory.
You need to set the build option to "Build" to actually create a .xnb file.
Regarding to the other post you received a "NullReferenceException" in the "TiledMapTilesetImporter", when trying to build the map.tmx file, so it seems that some important object inside the TiledMapTilesetImporter need to be instantiated first.
I don't know what your map.tmx file contains, but maybe there is something missing whereby this important object can't be created.
But i'm just speculating, as I don't know the TiledMapTilesetImporter class.