[flexcoders] Need help passing data to a title window

[Mark]

from the code below can any tell me why I get this error?  1119: 
Access of possibly undefined property myExcelDG through a reference 
with static type mx.containers:TitleWindow

I'm trying to pass data from one dataGrid to a dataGrid on the 
titleWindow.  Any ideas?

public var dgExcel:TitleWindow;
private var windowWidth:Number;
//
private function showWindow():void {
        trace("WIDTH " + this.width);
        windowWidth = this.width;
        dgExcel = excelPopUp(PopUpManager.createPopUp( this, 
excelPopUp , true)); 
        dgExcel.x=50;
        dgExcel.y=50;
        dgExcel.width = windowWidth - 100;
        // Pass a reference to the TitleWindow container
        dgExcel.myExcelDG.dataProvider = 
projCatHolder.allProjectsView.myDG.dataProvider;
}
private function onAppResize (oEvt:Event):void {
        var windowWidth:Number = this.width;
        if (dgExcel) {
                dgExcel.width = windowWidth - 100;
        }
}