I have an external hard drive set up for backing up with Time Machine on my Mac. It has been working well for about a year. Now when time machine tries to back up it tells me the external disk is read only. The hard drive does mount to the computer and will let me open the Time Machine folder. When I am in disk utility it also sees the external hard drive but will not let me click on repair disk permissions. The only thing that I can add is that we had a power outage in the middle of the night recently and maybe that had something to do with this? Any thoughts on how to get this drive back to read and write? The drive has not been ever used on a windows machine or use on any other computer. One day it was read/write next day read only. Thanks!