Printing without dialog box

Hi,

I'm making a maths learning app for kids using AS3. I have a page with a certificate and want to make a button which prints to the default printer with no printer dialog box.

The code I have;

pLvl1Print.addEventListener(MouseEvent.CLICK, printContent);

function printContent(evt: MouseEvent) {

  var pj: PrintJob = new PrintJob();

  var started = pj.start2(null, false);

  if (started) {

  pj.addPage(content_mc);

  pj.send();

  };

  pj = null;

}

The error I get:

The problem line of code is in bold.

Can anyone point me in the right direction? The other post's I've found don't seem helpful to me.

Thanks

Jack