Import mx.controls

For some reason, I get a compile time error everytime I try to import mx.controls.* What could be the cause of this?


package src {
	
	import mx.controls.MenuBar;
	
	public class MainMenu {
		
		public function MainMenu() {
			
		}
	}
	
}

gives me this error:
1172: Definition mx.controls:MenuBar could not be found.