Black Plague (spoiler): door won't open

[Fortigurn]

Ok, I picked up the mystery chemical, activated the emergency shutdown, made my way through the tunnels, flipped the switch for the exit, headed through the automatic glass sliding door, can see that the exit has the green light on, and... can't get through the exit.

The door just won't open. I have about half a minute to go, and despite trying to encourage it to open by exiting and re-entering the automatic sliding door, the door refuses to open. The countdown ends, I die. I've tried several times in a row, and it never opens. Suggestions?