My computer is stuck on the gray screen with the Apple and the status bar, so I am attempting to back up from my disk utility onto an external hard drive before I take it into the Genius Bar to be looked at, and when I try to create the new image it says unable to create back up.dmg (input output error).
MacBook Pro, iOS 6.1.4
There is something possibly physcially wrong with the internal drive or the MacintoshHD boot partition's data, likey a failed file struture due to shock damage or failing sectors.
Instead of using Disk Utility and grabbing the whole thing along with corrupted areas, rather instead do this and grab just the files you can.
.Create a data recovery/undelete external boot drive
You also might find you can repair it in place and even boot the computer into Safe Mode to copy files easier that way.
Unable to create backup.dmg input/output error
