You might be able to get it to work by adding it manually... This has worked for me once when maps crashed for me.
Ok I'll try to explain it clear as possible...
Ok first- Go into mapmaker and on the first tab, the map tab, type in the map name you want under 'Map Name' and 'Map Display Name'; then click save.
Now close FH.
Next- Go to your FH terrains folder, /C->Feral Heart->Media->Terrains, and look for a folder with your map's name. Put your heightmap picture into this folder.
Then inside the folder look for a file 'mapname.CFG'. Open this file in Notepad.
Once you have it open, look at the 2nd line of text it should say 'Heightmap.image=defaultTerrain.png'. You want change that to 'Heightmap.image=YourmapnameTerrain.png'. Save the file and close.
Go into mapmaker again, find? your map in the list at the bottom the Map tab, and click load. It should load with your heightmap, if done correctly.
Hope this works for you! :3
If not, I am unfortunately out of ideas x3.
