The SpaceX Falcon 9 rocket with the Dragon capsule. Image source: SpaceX.
At 1:15 PM EDT, SpaceX issued this brief press release in e-mail:
At this time, a May 7th launch appears unlikely. SpaceX is continuing to work through the software assurance process with NASA. We will issue a statement as soon as a new launch target is set.
I found this a bit odd, because last week NASA and SpaceX proclaimed they were happy with the last software simulation and were ready to launch on May 7.
There's some speculation that this may be due to the Soyuz TMA-04M launch on May 14 sending three Expedition 31 crew members to the International Space Station. If SpaceX has to delay or runs into trouble approaching the ISS, such as the Dragon fails and becomes a derelict, it could become a navigation hazard for Soyuz.
So perhaps this is just NASA's way of preferring they wait until after Soyuz docks at the ISS. Just my speculation.