Have you considered these?
- You have not bought a Head Texture item from the Torishop.
- Your texture is an RLE compressed .TGA. This can be toggled in most programs by unchecking a box when saved.
- Your texture is black and white only. This can be fixed by adding one or more colored pixels to the head. If you want to keep the black and white look, you can place the colored pixels at the very bottom of the texture.