Did you make sure that you have the absolute black and white included in your map? Sometimes I just used shades of grey and didn't use black or white to mark the lowest and highest points in the map, and it crashed because of that, it's really irritating, but make sure you have darkest black and the brightest white you can get and that might solve your problem. Otherwise, you could try copying your mask and replacing it into the watermill file, it will mess up your opening screen, but it should get it working, which is what I had to resort to for a map that didn't seem to want to load >3>