This is really a question for Wadronate, but I can tell you from experience that the 32 bit version of Wilbur has difficulty handling files sizes in excess of 4000x4000px (300dpi). Waldronate suggested to me that the 64 bit version could better handle larger files, but I haven't been able to get it to work on my system. One trick you can use with larger files (though perhaps not with the file size you are using) is to crop out the sea. Of course, that assumes you are working with on a map of a landmass surrounded by a body of water; if this is not the case then this technique will not work. If so however, cropping out the sea will reduce the file size. Once you've finished running the land through Wilbur then you can enlarge the canvas of the image back to it's original size in GIMP or PS. OK, I'll stop talking now and wait for Waldronate to come and clear this up better than I can.