The first crewed launch of Boeing’s Starliner capsule has once again been called off, this time after an automatic hold was issued by the ground launch sequencer less than four minutes before liftoff. As a launch commentator explained during NASA’s livestream, the ground launch sequencer is the computer that takes over the terminal count and essentially launches the rocket. “The reason for that hold is not known at this time,” he said. Starliner’s next chance to fly is tomorrow at 12:03PM ET, but whether it does will depend on the outcome of the team’s investigation into today’s issue.

In a brief update, NASA said the launch was scrubbed “due to the computer ground launch sequencer not loading into the correct operational configuration after proceeding into terminal count.” Why this happened, though, remains unclear. “The ULA team is working to understand the cause,” NASA said.

It’s been delay after delay for Starliner, which was initially supposed to take its first flight with astronauts on board back on May 6. If it can’t launch on Sunday, it’ll have other opportunities on June 5 and June 6. The mission, in which the craft will deliver astronauts Butch Wilmore and Suni Williams to the International Space Station for a brief stay before bringing them back home, is meant to validate Starliner as a viable crew transportation system.