Just got warning above, along with a Time Machine notification "Backup Not Completed. Time Machine couldn't back up to "My Passport for Mac". Pretty sure this means my WD Passport for Mac external HD is going down for the count, and that I need to get a new HD for use with Time Machine. One of the things I don't understand is what the notification means when it goes on to say "Back up the disk and reformat it as soon as you can." Does this mean to somehow back up the current, presumably bad HD to a new HD? How do I do that? And what does "reformat it" mean in terms of reformat what? I gather that since the warning says the I ca still open or copy files on the disk (old WD My Passport I presume), that I am to copy that earlier Time Machine back up to a new drive, as opposed to just hooking up a new HD to the computer and initiating a new backup. But I am old, it is late, and I am confused!!