I have the same problem. I can't play the game.
I also noticed when I activate only one mod (combat extender) the error message becomes " Failed to load the main menu from combat extender mod. The main menu in that mod requires the level. make sure to clear any local mods and try again. If the problem persists, please contact Larian support.""
I fixed the problem.
I removed the files in %localappdata% under the larian studios folder and it fixed itself
