I Dont know why u becomes this Mistake... But u can create these Files with Gimp oder Photoshop or like other.

I Know its not the Best Method , but ure Game works ^^

cYa Angel

Tutorials:
[Blender]Terrain creation ENG/GER
[Blender]Low Poly Tree Modeling
[GIMP]Create a Texture for Terrains
CLICK HERE