Whats wrong with my class!

Hi!

can someone PLEASE tell me why this isn’t working:

Box.as


class com.joelfinnstrom.Box {
    private var w_i:Number;
    public function set klas(w:Number):Void {
        w_i = w;
    }
}


my fla:


import com.joelfinnstrom.Box;
var b:Box = new Box();
b.klas = 20;
trace(b.klas);

the error:
Error Scene=Scene 1, layer=Layer 1, frame=1:Line 3: There is no property with the name ‘klas’.
b.klas = 20;

Error Scene=Scene 1, layer=Layer 1, frame=1:Line 4: There is no property with the name ‘klas’.
trace(b.klas);