I cannot rename or add any files (drag or File>Newfolder) on a bunch of files on my external harddrive. I think that it is because I created those files on my old mac (which I have sold). If I Get Info for drive and under permissions check "Ignore Ownership on this volume" then I can move/rename files again. But the thing is I need to have Ignore Ownership unchecked because I use the drive for backup (otherwise it won't copy certain files if it is checked). What do i need to do?