SpaceShipOne roll - Pilot error
According to spaceflightnow - http://www.spaceflightnow.com/ss1/status.html
"Mike Melvill just told reporters gathered at the runway that it was pilot error that caused the unplanned roll during the rocket engine firing of today's launch. He said SpaceShipOne performed properly and he was never worried during the flight, knowing he could damp out the roll motion. Once he knew the 62-mile target altitude would be reached, he commanded the engine to shut down. The cutoff occurred 11 seconds early. "