AS3 Cannot use mx Type in MXML when using a class

I have some issue which I cannot solve in AS3.

I have a simple application with a myApp.as and a myApp.mxml, now I moved all my function to a class called App.as I get errors on types I miss.

myApp.as:

    public function init():void {

    myApp = new App();

}

classes/App.as

    package classes

{

..

..

[Bindable] public class App

    {

..

public function cam {

...

myWebcam.attachCamera(camera);

..

        }

    }

}

myApp.mxml:

    <?xml version="1.0" encoding="utf-8"?>

<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml"

                xmlns:ns1="components.*"

                xmlns:ns2="*"

                xmlns:gauge="components.gauge.*"

                width="800" height="600" applicationComplete="init()" backgroundColor="#FFFFFF"

                layout="absolute">

    <mx:Script source="myApp.as" />

            <mx:VideoDisplay id="myWebcam" x="800" top="0" width="800" height="600" borderColor="#FFFFFF"

                             borderStyle="none" >         

            </mx:VideoDisplay>

</mx:Application>

This is kinda rough what I do at the moment where I get an error on:

myWebcam.attachCamera(camera);

TypeError: Error #1009: Cannot access a property or method of a null object reference.

When I had all my functions in myApp.as I never got this issue and I got my Camera in myWebcam. I get the feeling that my whole myApp.mxml is not loaded now I moved to a class ?

I have tried with parent(s) that might be around myWebcam but this doesn't seem to be the problem or at least not fix it.

My class complains about myWebcam not having a propery set, but when I make it a public variable like:

public var myWebcam:VideoDisplay;

The error goes away, but it's still a that null reference error.

What can cause this move from myApp.as to my class generating this "error" ?

I placed a trace in my mxml before my <mx:VideoDisplay id="myWebcam"... and it seems to be loaded up front of the script