Dynamic text field in embedded movie

programming flash
1

Hi I have main timeline and then have a small movie clip in which there is a dynamic text box and my actionscript.

myVars = new LoadVars();
myVars.load("http://preview.domain.co.uk/inc/loadVars.php");

myVars.percentage

myVars.onLoad = function() {
    text_box.text = this.percentage;
};

but when I play the movie it doesn’t work. However if I move the dynamic textbox onto the main timeline along with my actionscript it works.

Please can someone help i need to get this working asap