Why isn't my .p file working when I run the .m function?

FIrst of all, this use to work just fine when running the .m file. However, I went to view a .p file and when I went to "Open With", inadvertently failed to check the "Always use the selected program to open this kind of file". Now my .p file won't run from the .m function that is used to call it because it's selected for that other program.