possible bug

[jaaj302005]

if you add an active as a backdrop ladder then later change it to a non obstacle by pressing a key it will work if you run the frame but not in flash.

[Francois]

You mean by pasting it in the background?

[jaaj302005]

yes.

[Francois]

I think, that you have to drop somewhere in your application (even out of the screen) a background object with an obstacle proprety : this will force the collision mask to be created when the frame starts.