[Kittah]

Thanks for the tips all, but that's basically what I've already done... it seems as though Graal just doesn't like my tile image, despite it being an 8-bit .png as required.

As far as saving as .gif and then converting, it's the easiest method for me as I don't know how to set the image to 8-bit when saving as a .png in Gimp whereas saving it into .gif works fine.