Null Object not Null; What am I missing?

My problem is pretty simple (I hope). I am trying to add an EventListener to a MC, but I am getting the 1009 error. My script is referencing a MC that does exist. I have verified that my code is typed correctly, and that my instance names are correct.

The gist of my project is this:
I am creating a portfolio site. On the first frame I have my main navigation (well, it’s actually not the first frame. I alpha-fade everything in so it’s really the 6th or 7th, but I’m not sure how pertinent that is). The main navigation works fine (5 movie clips, fyi). Clicking them will move to a different frame, and the information and sub navigation for the frame will fade up. It is the sub navigation that I am having trouble with.

Here is my script for the sub nav with the error beneath:

trace(“well…the stop works”);
portfolioNav.pWebNav.addEventListener(MouseEvent.CLICK, pressWebNav);
trace(“this is more than I expected”);
function pressWebNav(event:MouseEvent):void {
var webStuff:Loader = new Loader();
webStuff.load(new URLRequest(“portfolioItems/webPortfolio.swf”));

well…the stop works
TypeError: Error #1009: Cannot access a property or method of a null object reference.
at out/frame20()[out::frame20:3]
at flash.display::MovieClip/prevFrame()
at personalSite3_fla::Header_1/ef()[personalSite3_fla.Header_1::frame1:22]

As you can see, it doesn’t even get to the function before it gets thrown off. I have verified that the instance names are correct. The script and the MC I am trying to add it too [I/]are[I/] in the same frame, which is what’s stumping me. Normally you get 1009 when the object you’re trying to reference is not there, but mine is!!

Obviously there is something wrong with my EventListener. I am not sure what else do; there is a gap in my understanding of AS. Any help would be greatly appreciated!