I have done that but after a couple seconds of loading, I get this message:
Python: Traceback (most recent call last):
File "C:\Program Files\Blender Foundation\Blender 2.91\2.91\scripts\addons\io_object_mu-master\import_craft\import_craft.py", line 106, in execute
return import_craft_op(self, context, **keywords)
File "C:\Program Files\Blender Foundation\Blender 2.91\2.91\scripts\addons\io_object_mu-master\import_craft\import_craft.py", line 80, in import_craft_op
obj = import_craft(filepath)
File "C:\Program Files\Blender Foundation\Blender 2.91\2.91\scripts\addons\io_object_mu-master\import_craft\import_craft.py", line 60, in import_craft
part = gamedata.parts[pname].get_model()
File "C:\Program Files\Blender Foundation\Blender 2.91\2.91\scripts\addons\io_object_mu-master\import_craft\part.py", line 64, in get_model
self.cfg, loaded_parts_collection())
File "C:\Program Files\Blender Foundation\Blender 2.91\2.91\scripts\addons\io_object_mu-master\model\model.py", line 49, in compile_model
obj = mdl.instantiate(f"{name}:submodel", position, rotation, scale)
AttributeError: 'NoneType' object has no attribute 'instantiate'
location: <unknown location>:-1