Mimicing a "close button"

I have a draggable, empty movieclip (container.mc) set as the target for three external movieclips which are loaded from three separate buttons on the stage. I also have a fourth button (unloadButton) on the stage that unloads the container.mc from the stage. Everything works as planned, the three buttons load the external mcs into the container.mc, the container.mc is draggable around the stage, and the unloadButton unloads the container.mc from the stage.

Now I want the unloadButton to be a PART OF the container.mc so it follows it around the stage and works like most “Close” buttons do. The unloadButton simply has the following action:

on (release) {
unloadMovie(“container.mc”);
}

When I place this button into a layer of the container.mc, it doesn’t work (but it works fine when it’s simply on the stage by itself).

Any suggestions?