Hello, I've researched and looked at other forums here but no one's situation seems to be like mine regarding backing up Time Machine to my external drive. I have plenty of backups I've done in the past on this drive with no problem. The drive has plenty of space and is partitioned. It usually runs right away when I plug it in. For whatever reason (possibly the upgrade to Yosemite since my last TM backup) I can no longer back up to this drive. When I open Time Machine through System Prefs - I cannot click on anything to back up to. When I go to Options, the ED is grayed out and "excluded." All I want to do is perform a backup like I have always been able to. Can someone please help me I included some pictures.