[F8] XML and MovieClips

Am I missing something here, basically the app loads three random images and a related caption from an XML.. the image across the page, when clicked the image expands and fades displaying a caption behind. The code works but every once and a while it breaks not simply switching the movie to the text without any animation, i've tried tracing all the variables but can't see whats causing it:

http://www.roptix.co.uk/test/test3.swf - what i've got, click the images a for a while and eventually one will not work properly, but then some still will.

code:

---

var cnt = 0;

var n = 0;

my_xml = new XML();

my_xml.load("data.xml");

my_xml.onLoad = runthis;

my_xml.ignoreWhite = true;





function SwitchMovie(i, n){

	trace(i+"-"+n+"-"+cnt)

	

	_root["container"+n].onPress = function(){}

		

		imagetext = my_xml.childNodes[i].childNodes[1].childNodes[0].nodeValue;

		_root["container"+n].createTextField("desc"+i, this.getNextHighestDepth(),-50,100,200,100)

		_root["container"+n]["desc"+i].text = imagetext;

		myformat = new TextFormat();

		myformat.size = 20

		myformat.align = "center"

		_root["container"+n]["desc"+i].setTextFormat(myformat);

		_root["container"+n]["image"+i].onEnterFrame = function(){

		_root["container"+n]["image"+i]._alpha-=10

		_root["container"+n]["image"+i]._xscale+=10

		_root["container"+n]["image"+i]._yscale+=10

		_root["container"+n]["desc"+i]._xscale+=20

		_root["container"+n]["desc"+i]._yscale+=20

		

		if(_root["container"+n]["image"+i]._alpha < 0)

		{

			unloadMovie(_root["container"+n])

			cnt--

			runthis();

		}

		}

}



function LoadImage(i, n){

	imageurl = my_xml.childNodes[i].childNodes[0].childNodes[0].nodeValue;

	_root["container"+n]["image" + i].loadMovie(imageurl); 

	_root["container"+n].onPress = function(){

		SwitchMovie(i, n);

	}

}



function runthis(){

		if(cnt < 3)

		{

			tspeed=random(10) + 1;

			i =random(my_xml.childNodes.length)

			_root.createEmptyMovieClip("container"+n, _root.getNextHighestDepth());

			_root["container"+n].createEmptyMovieClip("image"+i, this.getNextHighestDepth());

			_root["container"+n]._x=-30;

			_root["container"+n]._y=random(400);

			_root["container"+n]._xscale = 50;

			_root["container"+n]._yscale = 50;

			_root["container"+n].onEnterFrame = function(){	

			this._x+=6

			if(this._x > 600){

				unloadMovie(this)

				cnt--

				runthis()

			}

			}

			

			LoadImage(i, n);

			n++

			cnt++

			runthis()

		}



		

}

---

Apologise for the messiness of code, i am relatively new if anyone can offer an obvious improvements i'd appreciate it, but why is that working most the time but then on the odd occasion not?