Ummm not saying yours is wrong we might have different directory structure but my path is not /mnt/sdcard/extsdcard/ its /mnt/media_rw/1234-5678/mygame.img if navigating from the mnt folder in the root directory. Double check if you can and see if yours is . My internals is /mnt/sdcard/ so there may be some confusion because logically id assume your path or somthing similar if i didnt look through the mnt folder first.