I am having the same issues with my macbook pro. So yesterday I went to Apple to get some help (I was there for an hour). What they said is to first going onto the external hard drive you are using to back up and delete the file that says current or running or something like that (it is under the folder for your computers backup. you should also see folders dated with your last backups in that folder.) To delete that file you may have to restart your computer to be able to fully delete it (after you put it in the trash). That didn't get the issue for me, so then he had me go under disk utility and select my macbook pro's hard drive and run repair disk permissions. Then try deleting that file that is on the external hard drive again and give time machine another shot. (this also didn't do it for me) So Apple said if that didn't work to reset home folder permissions and aci's. To do this you restart your computer while holding command r down until the apple logo appears. Then the computer starts into a weird looking mode. (it will almost look like it is starting normally, but don't worry, it isn't) Then you go to the top bar and select the utilities drop down menu and open terminal. Then type resetpassword (yes, one word) and that will open a new window and you pick your internal hard drive then you select the user and then at the bottom of the window, you can reset the home folder. This is the last thing they told me to try, but it didn't work for me either. I am still were I started, except for a wiped external hard drive (the guy at Apple wanted to do that just to make sure it wasn't the drive, but I don't think it wasn't necessary). If anyone has some ideas on where to go after this, please help me.