During the first test, to which the media did not have live access, there was a problem with a safety system that uses fans to maintain pressure and keep dangerous gases out of the mobile launcher. “Technicians are unable to safely proceed with loading the propellants into the rocket’s core stage and interim cryogenic propulsion stage without this capability,” NASA wrote. In the second test, a different issue occurred with the system: when the team was getting ready to fill the rocket with fuel, something went wrong with a panel controls a vent valve on the rocket. This happened late on April 4, so the decision was made to stop the test for the night and to investigate.
The next day, NASA announced that, “Inspections after the second test showed the vent valve that prohibited the team from proceeding with loading liquid hydrogen was configured physically in a closed position, which prevented it from being commanded remotely to an open position. The valve positioning has since been corrected.”