Press f1 (You need a dev environment) and check Show Debug Messages. Look at the lower left corner when you enter the area that calls the function and check if you see the message "Grunt should now move".
With propforce, you generally need to use really big numbers to make it have any effect- otherwise, the innate forces of the in-game gravity will just make it stay there. I generally have to use numbers in the thousands if I want to do something as simple as slowly push open a door.