I asked a friend at ZLA what he knew, and he said nothing went down, they were just getting a lot of error messages and as a precaution they decided to issue ground stops until they could figure it out. There were two technical problems but they were apparently properly handled by ERAM. One was a cut fiber optic line in SoCal that was interfering with flight data transfer to some other facilities (adding to controller workload because some things like handoffs had to be done over the landline).

The second wasn't from a U2, just its flight plan which possibly as a result of the data transfer problem apparently had an altitude of "0" for the flight plan altitude. The long-term conflict probe (EDST) was then checking every few moments for everything from its current FL600 mode C down to the 0 assigned altitude along its winding flight path, checking against probably several hundred VFR and IFR targets in SoCal all going in different directions. This stretched the limit of the CPU or some part of memory and spewed out warning messages, although didn't cause a crash. All those messages on top of the known data transfer failures spooked ZLA enough to decide to ground stop. If there was only one problem or the other, or ERAM wasn't so new, they probably wouldn't have reacted like that. It was just a precaution apparently.