"iTunes could not connect to this iPhone. This device is no longer connected."
I was getting the same problem yesterday with both my iPads. Finally gave up and re-booted the Mac -- problem went away. Might be worth a try.
The problem I had was the lightning cable. I changed the cable and the problem was solved.
My friend who encountered same problem mentioned he just re-booted the Mac and the problem wnet away, you could give it a shot.