Based on the error and the example I'm guessing that you are
trying to build an AS3 project instead of a flex / air project? Or
maybe just an ordinary flex project? In which case you will get the
exact error you mentioned below as the necessary resources for
dealing with Native Windows are only available if you build an AIR
If you build a new AIR app (or use an existing one) and then
add the NativeWindowResizeExample class to the AIR app it should
then compile perfectly for you.