AKA lost constrol of the engines. It could of landed in a field and it would of still crashed. Man there are so many armchair rocket scientists.
[1] http://aviationweek.com/space/spacex-checks-throttle-valve-a...
when the rocket touched on the barge, thrust vectoring couldn't rotate the rocket anymore, since legs become a fixed pivot. and rcs didn't had enough trust to upright the rocket.
now I don't think the issue is as easy as 'rcs didn't had enough thrust'
what looks like is that the control system minimized vertical/horizontal velocity but allowed the rocket to touch down with too much rotational momentum.
whether this was caused by software or hardware has to be seen. if they are storing the landing fuel in the same storage as the ascent fuel, sloshing may be a big factor.
but I honestly have no idea, just like the speculation.
Honestly, I've had several missions to Jove which have ended in disaster because my keyboard died during orbital insertion.
And that would be so annoying. It's no trivial task to get all the way out there and bleed off all that velocity.