Yes I have read the *read this if you have trouble with heightmaps* thread. A dozen times. I have also made a dozen successful heightmaps.
That's why this is annoying. Because it might just be that my computer sucks and there's absolutely nothing I can do to fix it.
So I got some new brushes yesterday and had fun making new heightmaps. I made some heightmaps, put them into mapmaker, and they worked, but they kind of sucked. So I made two new ones today - one with the new brushes, slightly blurred, and another version of the same one super-blurred, because I didn't know how smooth I wanted it. After a certain point of smoothness the rivers start turning into divets and mountains into molehills, so I usually have two copies.
After trying to put the heightmaps in six or seven times, I finally realize "Geeze.....I did everything wrong. XD 2000x2000 res, RGB mode, .JPG files." So they are now 513x513 grayscale .PNGs. Saved into the terrains folder.
I open FH mapmaker and I can load some of the other heightmaps I have made, and can load the slightly-blurred heightmap. Sometimes. Sometimes it just crashes. Other times it crashes when I try to resize the map. Other times I get this, no matter what heightmap I have loaded.