need help with flashvars as3

I am creating a website for my 3rd year university project, i have created a profile page that displays information for each member, however i would also like to include a flash player the streams the music they have uploaded.
i have also created an xml file embedded with php that sorts the tracks title and location, i have called this playlist.php. i have tested this using members usernames and it seems to work, however when i try to use flashvars to generate a username it always seems to go wrong??

(not the complete code)

var keyStr:String;
// Claim valueStr variable as a string
var valueStr:String;
// Create the paramObj Object and set it to load parameters
// from the root level being sent in by FlashVars externally

var paramObj:Object = LoaderInfo(this.root.loaderInfo).parameters;

valueStr = String(paramObj[keyStr]);

loader.load(new URLRequest("http://localhost/playlist.php?"+keyStr+valueStr));

I could be wrong, but I think you are basically redeclaring the variable, which would erase the flashvar version. Have you tried without declaring it? Its a string by default.