Ngui: how to insert text on a label via javascript?

I just spent the last two hours searching on how to insert text on a label via javascript. It should be easy, I guess... I wanted to make a health bar and a timer. Can somebody help?

I wrote this code but it just gives me the error "The name 'UILabel' does not denote a valid type":

 var scoreLabel : UILabel;
 
 function Start () {
 scoreLabel.text = "just testing";
 }