of things like propellant voids (like mentioned in the article) or insulation failure. Both things have been known to cause spectacular explosions, even for vehicles like the Delta II and Titan IV. An explosion immediately on ignition is often an indicator of an overpressure caused by a void. If they can get their consistency and quality control problem resolved, then they can make their system work. They might want to see if they can get their engines X-rayed before their next attempt. That picture of the dummy's head isn't exactly a good selling point for their system.

While I'm looking forward to the X Prize and the later X Prize Cup, I just hope people aren't killed needlessly over things that have been known in the aerospace community for decades.