Map Maker keeps crashing

[Asheyx]

Ok, so I already read Delay's help thread about Map Maker issues, but it didn't help me at all. Well, I don't even know what I'm doing wrong, but maybe you know.
My problem is that my Map Maker keeps crashing when I try to load height maps. I made sure that they are grayscale, square, have only 1 layer and are saved in .png format. But it doesn't work. I tried to load just a blank height map, and that worked. Then I added only 1 little river, and my Map Maker crashed again.
I made maps before, and it all worked perfectly. Any suggestions what I should do?

[Rimfrost]

If it is in same size both side, example: 513x513 and still dont work, try to switch to RGB and then greyscale again

[Asheyx]

Do you mean drawing the height map in RGB and 'transform' it into Grayscale then?

[Ruby1234]

She means once it's already drawn, switch it from grayscale to RGB and back to grayscale again.

Requirements:
513x513
Grayscale
Is now, and was always one layer

Things to try:
Switch the format to something else, then back.
Copy the image, close out the image so the image program is blank, and paste it in, then flatten it, and save it.
Switch it from Grayscale to RGB. then back to Grayscale.