External Images not loading in Flash 7 player

I'm have a site that has a Flash intro that loads random images from a directory. I published the movie for Flash 7 player in MX 2004.

http://www.portcityarch.com

If you view this on a PC in IE6 (or on a Mac with any browser) with Flash Player 8 - it works as expected - the images appear in the boxes that decend from the Port City Architecture title bar.
If you try the same site on computers with the Flash Player 7, the images don't load.

There's a sub-directory called: "portimages" - that contains several images for each category. The movie starts out by selecting a random number which shows that particular set for each category. I don't believe I'm using any crazy code.

Randomizer code:
this._lockroot = true;
_root.randomNum = 4;
_root.myClipNum = (Math.floor(random(_root.randomNum)+1));

Code to load external image - this code is in each movie clip for each category - there's a movie clip called myPic_mc which is meant to be the container of the image:
loadMovie("portimages/pic01_" + _root.myClipNum + ".jpg", this.myPic_mc);

Can someone help out?

Thanks! Chris