I have all the DLCs. They show up both in Steam's installed DLC list and the game's module screen as active, however now that you mentioned it I tried starting a new Embers campaign and I get a similar error. I can get to the character creation screen, but when I click "Play" it just throws this error and a black screen. I tried reverting back to non-beta version and both Embers and the book seem to work fine then. So I'm guessing there's some sort of issue with the beta patch and Embers content in general?
All DLCs active:
Error I get when starting an Embers campaign:
