unloadMovie(); causing buttons to break

programming flash
1

When a button is clicked in my main movie, a swf loads in a container clip. When the “BACK” button is clicked on the loaded .swf, the .swf is unloaded but the buttons I have on my main timeline no longer work. Any idea why this is happening?

code on main timeline of main movie:

this.main.nav.project.onRelease = function() {
 	trace("Project Clicked");
 	_level0.main.play();
 	_level0.container.loadMovie("project.swf");
 };

code on main timeline of loaded .swf file:

this.backNav.onPress = function(){
 	trace("Back Button Pressed");
 	_level0.main.play();
 	_level0.container.unloadMovie();
 }