That's weired. Windows XP puts a thumbs.db file into every folder with an image(MacOSX does it still today)
Did you tried to delete the build folder? And check if you don't have any thumbs.db file floating around. If you find one, delete it, delete the build folder and try building.
Did you tried to delete the build folder? And check if you don't have any thumbs.db file floating around. If you find one, delete it, delete the build folder and try building.