Try 513X513 if 512X512 doesn't work. Also, try not to press 'enter' when you insert the map, just click on something else and it will appear. Another thing: did you make sure that you saved it in the Feralheart, media, terrains folder? If any of these don't work try to restart your computer and try again. If that doesn't work, I would reinstall Feralheart and try again again. I hope I could be of help ^^.