CarController Script Error

Hello,

Im trying to get this script to work http://www.unifycommunity.com/wiki/index.php?title=WheelColliderSource-CarController but i keep getting an error.Here is the error Assets/CarController.cs(26,13): error CS0246: The type or namespace name `WheelColliderSource' could not be found. Are you missing a using directive or an assembly reference?.Can anyone help me please.