NASASpaceflight.com reports on a failure of an AJ-26 engine during a static fire on Thursday:
One of the AJ-26 engines set to launch with a future Antares rocket has failed during testing at the Stennis Space Center on Thursday. Sources claim the engine “exploded” on a Stand located in the E Complex at the famous rocket facility. The failure is currently under evaluation, although it may delay the next Antares launch that is tasked with lofting the the ORB-2 Cygnus to the International Space Station (ISS).
Not a lot of details at this point. I’ll update this post as more information becomes available.