How to use child class with loaded external swf?

[yashiharu]

I would like to load external child swf into the parent swf (under same directory). I did try, the child loaded but the class in it didn't work.
1) How can i load the class of child swf?
2) How can i unload the class of child swf?(becoz there could be many ext. swf with different class)
thx

main.fla

function startLoad(){
    var mLoader:Loader = new Loader();
    var mRequest:URLRequest = new URLRequest("game1.swf");
    var mLoaderContext:LoaderContext = new LoaderContext(false,ApplicationDomain.currentDomain);
    mLoader.contentLoaderInfo.addEventListener(Event.COMPLETE, onCompleteHandler);
    mLoader.contentLoaderInfo.addEventListener(ProgressEvent.PROGRESS, onProgressHandler);
    mLoader.load(mRequest, mLoaderContext);
}
function onCompleteHandler(loadEvent:Event){
    var keyManager:Class = ApplicationDomain.currentDomain.getDefinition("net.keithhair.KeyManager") as Class;
    addChild(loadEvent.currentTarget.content);
}

game1.fla

Code:
import net.keithhair.KeyManager;
keyManager=new KeyManager(stage);
keyManager.addKey(["a"], doSomething);
function doSomething():void {
    //do something  
}

Result:

Code:
TypeError: Error #1009: Cannot access a property or method of a null object reference.at net.keithhair::KeyManager/removeListeners()
at net.keithhair::KeyManager/addListeners()
at net.keithhair::KeyManager()
at game1_fla::MainTimeline/frame1()