Flash not getting vars from php

i have some code that works perfectly fine on one server, but on another, it does not. basically, all i’m trying to do is send some vars from my swf to a php file…the php file does its process…then the php file prints out variables which flash should take back. the php file is being called and receives the variables correctly (i know this because i’ve printed out the values to a text file)…it processes them correctly (again b/c of the text file, i know this), but flash keeps telling me that the variables it should be receiving are undefined. here is code i have…

flash

var dataSenderLoad:LoadVars = new LoadVars();
var dataReceiverLoad:LoadVars = new LoadVars();
dataSenderLoad.startNode = mc_from.selectedNode;
dataSenderLoad.endNode = mc_to.selectedNode;
dataSenderLoad.sendAndLoad("http://www.personal.psu.edu/users/n/c/ncc5012/portfolio/pathFinder/php/pathFinder.php", dataReceiverLoad, "GET");
dataReceiverLoad.onLoad = function(success:Boolean){
        if (success){
            trace("success!");
            trace(this.pathString);
        }
}

php

$startNode = $_GET["startNode"];
$endNode = $_GET["endNode"];
//do some stuff
echo $pathString; //$pathString = something like this...pathString=21,18,23,15

i have no idea what’s going wrong. and nobody that i’ve asked at the school (where it’s being hosted) seems to know either. any ideas what the problem might be?