Late 2013 iMac with 10.10.3. Unable to erase free space with any of the number of pass choices. Will act like it's going to and then tells me after as much as 2 hours that it is unable to create a temporary file. I have done a 3-pass erase recently with no problems, so I have no idea why now. I recently added an external back up drive, but it doesn't make any difference whether it is connected or disconnected, same fail message. I did a search and found a similar problem, but that poster received no replies. I will appreciate any and all help I can get. Thanks!