If you have SlideShowPro nested inside of one or more Movie Clips, SlideShowPro won't be able to correctly position itself to the top-left corner of the Stage when entering full screen mode. To resolve this, you can set up an event listener for SlideShowPro's onFullScreenChange event, and move the Movie Clip containing SlideShowPro to the top-left corner (thus positioning SlideShowPro where it should be full screen).

This also assumes that SlideShowPro is positioned at 0,0 inside of its parent Movie Clip. If it's not, you'll need to modify the positioning code below.

Stage.align="TL";
Stage.scaleMode="noScale";

var origX:Number = container_mc._x;
var origY:Number = container_mc._y;

listenerObject = new Object();
listenerObject.onFullScreenChange = function(eventObject):Void {
if (eventObject.data == "fullScreen") {
    container_mc._x = 0;
    container_mc._y = 0;
} else if (eventObject.data == "normal") {
    container_mc._x = origX;
    container_mc._y = origY;
    }
}
container_mc.my_ssp.addEventListener("onFullScreenChange", listenerObject);

In this ActionScript, container_mc is the instance name of the Movie Clip containing SlideShowPro.