This problem is unusual so i don't know the exact answer, but this happened once to ZombehKitteh and it was because she had too much objects groups with many meshes in a single map, and that ate all the video card memory.
Also could happen if you have an invalid mesh file or texture.
I suggest that you back-up your entire feralHeart folder and/or your maps and you try to delete complete objects groups from your map one by one by directly deleting the .object files, restart the game and to try to export your map each time you deleted one object group.
This is just to try to search wich object group could be causing a problem.
Then once you know wich one is wrong, you restore all the rest of them.
In the case your map is huge or has a lot of objects, make a back up of your map and try to delete half of the objects of it by editing the file yourmapnameObjects.cfg, just as a try, not permanently.
I hope this idea can be helpful.