At 30 minutes from launch, the Atlas V 531 launch of the Air Force’s Advanced Extremely High Frequency-2 (AEHF-2) was at T-minus 4 minutes in a built in hold. An issue with purging the Interstage Adapter compartment is being worked. It may be that a manual valve on the level 3 platform is out of configuration.
And 50 minutes after the launch window opened, ULA has announced that the launch has been scrubbed and rescheduled for 4 May 2012. The launch window will open at 11:42 Phoenix time (1842 UTC) and extend for two (2) hours. Weather is predicted to be 80% favorable for the launch.
The webcast from ULA begins about 30 minutes prior to 11:42 PM Phoenix time (1842 UTC). NASA video and mission events can be found here.