AS3: hitTest Help

I'm using this code to detect a collision with the movieclips circle and line, but it doesn't appear to be working.

if(circle.hitTestObject(line)){
// stuff
}Can someone please tell me what's wrong? Thanks in advance =D

I don't pretend to know about AS3, all of this crazy OOP, but here is some info that might be useful, do you have all of the imports?

http://www.foundation-flash.com/tutorials/as3hittesting/