Make sure the name of the map doesn't 'ave spaces. Like if ye were to name it The Big Map, ye could only put it as, TheBigMap. Spaces glitch Feral Heart and cause it to crash.
Also, make sure 'tis in grayscale and not RBG. It can tell even though ye may 'ave used only gray, black, and white.
Y'er height map can only be 513x513, so if it is one pixel off, it will crash.
I hope this helps, and good luck with the map making!