code doesn't work

I put the following code in AS3 but when I type in to the input the letter "a" it doesn't go to frame 3.

enter.addEventListener (MouseEvent.CLICK,NF);

function NF (event:MouseEvent) :void {

if (Ntext.text == "a") {

  gotoAndStop(3);

}

else {

  error.text = "X";

}

}