Dynamic class - little problem

dynamic class Box { // defining class named Box
public var width:Number = 15; // data members width and height definition
public var height:Number = 15;

// creating instance
var b:Box = new Box( );
// add dynamically the property of the instance

b.newProp = "hello world";
// enumerating properties
for (var prop in b) {
trace("propriete nom: " + prop);
trace("propriete valeur: " + b[prop]);

I want to obtain this as an output:

//propriete nom: newProp
//propriete valeur: hello world

I receive the same error as in this topic:

The error is:

Classes may only be defined in external ActionScript 2.0 class scripts.

I read this article from here:


I put the .fla and as file in the same directory and added it in ClassPath.

But still I receive that error.