macromedia flash flashcom: my code is simple :

application.onAppStart =function (){
trace("onAppStart")
}

I don't understand when it trace, it did it for a few times and now it doesn't.

any idea?

Keep in mind onAppStart won't fire if the application instance already exists.
From the docs:
Event handler; invoked when the server first loads the application instance.
You use this handler to initialize an application state. You can use
application.onAppStart and application.onAppStop to initialize and clean up
global variables in an application because each of these events is invoked only
once during the lifetime of an application instance.