Hello, there. I would suggest you uninstalling FH. It's a possibility that you have deleted the file temp.map and the folder temp who is located to the terrains folder.
The best solution: uninstall, delete and reinstall FH, but don't forget to back-up all your maps (the .map files and their folders), the objects (.object files), and all your meshes and stuff.
Replace your current temp folder with a working temp folder in FeralHeart>Media>Terrains from an untouched FH.
Good luck!