This morning's attempt to launch a Falcon 9 with a Dragon spacecraft was scrubbed when a high pressure reading was discovered in first stage engine 5. The launch vehicle is now being put into safe mode. The next launch window will be on Tuesday at 3:44 am EDT.
Marc's update: Here's my story and the post-launch attempt briefing video.
"Right up to t-minus 0.5 seconds it looked like there was going to be a launch. Unfortunately the Falcon 9 computer shutdown the rocket just as it was set to launch due to a high pressure reading on engine number 5, one of nine engines on the Falcon 9 first stage."