Why "if (Key.isDown(Key.ENTER))" is not working

programming flash
1 
var keyListener:Object = new Object(); 
 keyListener.onKeyDown = function() { 
    if (Key.isDown(Key.LEFT)) { 
 	  trace("test"); 
    } 
 }; 
 Key.addListener(keyListener);

The above code works perfect, but if i write ENTER instead of LEFT, it doesnt work, does anybody has any idea of whats going wrong?

Thanx