Mewtwo Strikes Back
You never, really never have to disable that option. Instead, you have to repoint the image you want to insert somewhere else by finding a free space area and putting the offset you found in the Image Offset when importing it into unLZ, making sure to have "Automatically fix pointers" enabled. To fix your screwed up ROM, see my tutorial in the Documents and Tutorial section, HackMew's Knowledge. The link is in my sig.