Alopex

I've been trying to create a third person character controller, to little avail. I copied and pasted the script from this page, replacing all instances of "App.window" with "window" (because I kept getting "attempt to index field 'window' (a nil value)"). Now, every time I try to run the code, I get "attempt to call method 'SetPosition' (a nil value)". I'm a little bit stumped as to why the code won't run properly. Any suggestions?