Lately when I tried to do a manual backup with Time Machine I would get an error. I can't remember exactly what the error was. All I remember is that it said it could not backup. Finally had time to spend to try and figure this out. I unplugged it from the back of my computer and plugged it into the front of my machine. That helped, for a couple hours. It backed up on the hour as is the norm and would back up when I did a manual backup but now it is not backing up on the hour anymore. By selecting a manual backup did that stop the automatic backup? I checked my setting and it is still turned on.