You should be in the Firmament when you start Chapter 2 of the scenario, not the Diadem. It sends you over to talk to Aurvael. If you’re already in the Diadem, make sure to start at Chapter 4 or later. And if you’re in the Firmament and it’s still giving you that error, try deleting the scenario and re-importing it. I had a weird error issue and that solved it for me.