Not sure if it's solely this mod causing that issue for you (as I was able to use it on an existing save with a few other mods).
When you add/remove/update mods that contain story scripts and try to load an existing save game, it has to rebuild the story to incorporate the changes on that first load (when you save the game after the long 10+ minute rebuilding process, it doesn't have to rebuild it when loading that new save, unless the story has changed again).
So usually if you get that error you got, that means something is failing when it's rebuilding. This error isn't solely from mods - people have gotten that error after updating the base game and attempting to load a previous save (as even in that case, it has to rebuild the story again if the update changed story scripts).
That may mean that one or more of your files may be corrupt. So maybe try and verify your cache? If that doesn't work, you could also try and reinstall the game. Getting that message on a new save is very strange.
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When you add/remove/update mods that contain story scripts and try to load an existing save game, it has to rebuild the story to incorporate the changes on that first load (when you save the game after the long 10+ minute rebuilding process, it doesn't have to rebuild it when loading that new save, unless the story has changed again).
So usually if you get that error you got, that means something is failing when it's rebuilding. This error isn't solely from mods - people have gotten that error after updating the base game and attempting to load a previous save (as even in that case, it has to rebuild the story again if the update changed story scripts).
Getting that message on a new save is very strange.