DiskUtility throwing "com.apple.disutility error 3" on "Operation failed with status 5" on Sierra while making image backup of main SSD
I just experienced the same problem while trying to clean install Sierra. I had the same error until I asked Disk Utility to mount the internal SSD. When I did so, it asked for the password to unlock the drive. After unlocking the drive, I was able to create the disk image.