TypeError: Error #1009: Cannot access a property or method of a null object reference

1

var lois_req:URLRequest = new URLRequest("mailto:address@comcast.net");

contact_btn.addEventListener(MouseEvent.CLICK, navlink);
function navlink(event:MouseEvent):void
{
gotoAndStop(“contact”);
}

loismail.addEventListener(MouseEvent.CLICK, loislink);
function loislink(event:MouseEvent):void
{
navigateToURL(lois_req, “_blank”);
}