The Big Picture:
Boeing is delaying the December 17 Orbital Test Flight (OTF) of the CST-100 Starliner commercial crew vehicle. The OTF is an uncrewed mission to dock at the International Space Station before it goes up with a crew inside.
The new launch date is December 19.
What happened?
Looks like there's an air supply duct problem somewhere between the bottom of the Starliner and the Centaur upper stage of United Launch Alliance's Atlas 5 rocket.