I initially did not add the new map to the MV version, but I was sure it still had the updated version of the plugin. Either way I wasn't getting the error you were having. Was it a consistent error upon map load or does it only happen at times?
Anyways, I have just pushed an update to the MV demo with the new Volley Pal map and ladder event. See if the error persists and If I did just forget to update the demo. If you have MZ, I recommend you using that one instead. MV has limited lines for script calls so I had to one line all of them, and it's not gonna be user friendly to look at and study.