Well during the landing processes, the booster ran out of hydraulic fluid moments before landing. The first stage got amazingly close to the ship, but didn't quite nail the landing. SpaceX actually released video of the landing attempt and it is phenomenal to see!!!
I can't stop watching it - it's addictive. Space X is calling it a "Rapid Unscheduled Disassembly", you can see Elon Musk's (owner of SpaceX) twitter dissection of the failure here.
(image from here)