TypeError: Error #1010: A term is undefined and has no properties

1

Ok, this is driving me insane.

I have my AS3 on the main timeline in the first frame:

import flash.events.MouseEvent;
import flash.net.navigateToURL;
import flash.net.URLRequest;

hero.btn_purchaseNow.addEventListener(MouseEvent.CLICK, getLink);

var url:String = "http://www.addresshere.com/";

function getLink(e:MouseEvent):void
{
    var request:URLRequest = new URLRequest(url);
    try {
        navigateToURL(request, '_blank');
    } catch (e:Error) {
        trace("Error occurred!");
    }
}

I have a movieclip called ‘hero’ sitting in frame(1) on the timeline.

Inside that movieclip is another movieclip ‘btn_purchaseNow’ which will act as my button. This button is animated with keyframes, and in every keyframe it shares the same instance name of ‘btn_purchaseNow’.

When I export my flash file or test, I get the following line in the output window:

TypeError: Error #1010: A term is undefined and has no properties.
    at Hero_fla::MainTimeline/frame1()

The issue is not an incorrectly named instance, I’ve checked.

Could somebody please suggest a reason for why my button will not work?