I have an older external HDD which is faulty and from which I can only read but not write onto. I wish therefore to transfer its contents over to a spanking new external HDD and then reformat the older faulty one. Trouble is, although I'm having no problem copying over large chunks of data from my MacBook's HDD onto the new external HDD, when I attempt it with files from the older External HDD, it says I do not have permission on the "backup drive". Huh? Please help!