[asheshouse]

Have a look at the map_c in one of the working modded maps.
You will see that it is a disected image file.

You need map_c tools. Request these from Fly_zo

These come with readme instructions.

You will rename your existing map_c.tga to Mymap_c.tga

Run transform.bat to pre-process the image.
This creates MWmap_c.tga

Then run disect.bat which creates NewMWmap_c.tga and MWmap_c.tga_table
Rename these to map_c.tga and map_c.tga_table after backing up any existing files if required.

You should then be good to go.