For the heightmap, did you use more than one layer? Also, what program were you using to make this?
I used about 2 for the terrain, and 5 for the mask, but I saved them as .png at the end. And I used Gimp.
Merge all of the layers so there is only one for both the mask and the terrain. If there's more than one, game crashes.
Also, make sure there's no alpha channel.