I'm trying to load a spritesheet into the program, attached below (xcom.png), but I get this error:
An error has occured during loading of the file: Index was out of range. Must be non-negative and less than the size of the collection.
Parameter name: index
I'm pretty sure everything checks out, from the size of the image to the exact colors used. I don't know what I could be doing wrong.
EDIT: In case it helps, the image was saved with paint.net with 8-bit bit depth, Median Cut quantization, dithering level 0, transparency threshold 128, not interlaced.
I also created another image file (fuck.png) with UnitSprite Studio, saved it, and loaded it again without problems. I did not touch that one with paint.net.