Well it could be your map itself. Make sure that you saved it as a .png and that it is in your C>FeralHeart>Media>Terrains.
Also a trick I was told is that you go into FH and map maker, name your map and save it and that automatically makes a folder in terrains. Make sure your map is 513 pixels by 513 pixels, that it's set for grayscale, and it's one layer. (if you're working with photoshop or gimp). Then when you're done just find your map folder in the terrains and save it there. So when you go back into the game and type the file into the HeightTerrain textbox, enter, and there should be your terrain.
Hope this helps