Check the properties (Right click) of the skin you have made. If it is more than 1.0meg, you didn't save it as an 8 bit BMP and it will crash the game every single time..
Been there, done that.
A FEW times
As Elbert said, change the mode to "indexed color", than 256 color, Local (adaptive) and that will save it as 8 bit color. "Adaptive" takes the color shades YOUR using and gives you 256 options. "Forced black and white" just makes sure you have a slot in your pallet for black and white. Adaptive saves ugly change overs to BMP files because it uses your samples to create a 256 color pallet.