I would guess the error comes from having both KGC_CustomCommand and Scene_MenuRedux. I removed the KGC_Custom Command script and the error went away, so that is where the incompatibility is coming from. If I looked at them closer, I would likely be able to diagnose the exact problem, but really, there is nothing the KGC script does that can't be done by Yanfly's Scene Menu Redux. I suggest you just get rid of KGC_CustomCommand altogether and see if you can set the menu up through Scene Menu Redux instead.