Probably this script new_system.m is called in the InitFcn or PreLoadFcn of your model (go to Model Explorer ->InitFcn or PreLoad function tabs, note that, if this is the case, then an asterisc will appear on one of them or both (e.g. InitFcn*), or in another of the tabs there: open the tabs with asterisc to check where new_system.m has been typed).
Remove the .m to execute the script (i.e. replace new_system.m, with simply new_system). The error should then disappear, as the script is now executed.
