Make sure that the map is flattened when you go to save it. If not trying moving it over to GIMP ( if you have that ) and then saving it again. Make sure 513 x 513 as well.
When you make the map, make sure its RGB when fill it in and that there are no blank areas before making it greyscale. I know I'm missing some parts but those are some things you can keep in mind when making the map c:
You can also check out this link here to see for some pics and other tips.
Click Me~! (http://www.feral-heart.com/index.php?option=com_content&view=article&id=6&Itemid=11)