As reported by engadget,
This won’t necessarily lead to a large delay, but it’s still an unpleasant setback for Virgin. This test would have been the last before a new test phase where the company would have specialists sit in the cabin to help improve the experience for passengers — some of the last steps before commercial service begins. If there’s anything more than a small delay, Virgin can’t start taking paying customers for a while longer.
The test was also supposed to be the first crewed spaceflight ever to launch from New Mexico, and the first from Spaceport America. Like it or not, the history making will have to wait at least a little while longer.
Early update on flight: The ignition sequence for the rocket motor did not complete. Vehicle and crew are in great shape. We have several motors ready at Spaceport America. We will check the vehicle and be back to flight soon.
— Virgin Galactic (@virgingalactic) December 12, 2020