Errors tend to be along the lines of
error: Cannot call BlockActivation() on a None object, aborting function call
stack:
[ (09010B77)].DN045_MonorailScript.BlockButtons() - "g:\_F4\Art\Raw\Scripts\DN045_MonorailScript.psc" Line 129
[ (09010B77)].DN045_MonorailScript.StartTrain() - "g:\_F4\Art\Raw\Scripts\DN045_MonorailScript.psc" Line 143
[ (09010B77)].DN045_MonorailScript.OnCellAttach() - "g:\_F4\Art\Raw\Scripts\DN045_MonorailScript.psc" Line 54
While this is a mod-added version I think it applies to vanilla as well, because the "OnCellAttach" code calls those functions without making sure the monorail has actually loaded first. I think it just needs a self.waitfor3DLoad() call at the start of the OnCellAttach function to resolve these errors.