Im not getting the crash you reported. Is obj_player_input in the room? That's the object that sets the input variables.
In any case, this project is very old and could do with a remake instead of patching.
I think it was a mistake for me to include things other than a battle system in the asset, and I added a version to work with the shop and inventory system (at someone's request), which just complicates the battle asset page with multiple versions.
The best thing i can do is just rewrite the battle asset, and shop/inventory asset to be as stand alone/plug and play as possible but i won't be doing that for a little while yet.