Error when doing Penelope Tutorial. Need Help

I just finished the joystick script and everything is fine but when I attach the Joystick script to the right joystick I get a "NullReferenceException" as an error. The script is perfect when it's on the left pad but when I add it to the right pad I get that error.

When I double click on the error it highlights this line of code.

gui.pixelInset = defaultRect;

I just needs someone to explain what that error means.

Could there be a second script or a GUI component you need to attach as well? Check both joysticks in the inspector and make sure they have all the same components.