Uncaught exception when I update window

Question

Hi All,
I want to show a progress bar while executing script.
and i am using the following code for that:
var win = new Window("palette", "SnpCreateProgressBar", [150, 150, 600, 260]);
win.pnl = win.add("panel", [10, 10, 440, 100], "Script Progress");
win.pnl.progBar = win.pnl.add("progressbar", [20, 35, 410, 60], 0, 100);
win.pnl.progBarLabel = win.pnl.add("statictext", [20, 20, 320, 35], "0%");
win.show();
                    while(win.pnl.progBar.value < win.pnl.progBar.maxvalue)
                              // this is what causes the progress bar increase its progress
                              win.pnl.progBar.value++;
            win.pnl.progBarLabel.text = win.pnl.progBar.value+"%";
                              $.sleep(10);
    alert('Done!');
win.close();
But I am having following error when I run it:
Can you please tell me why it is happening....
Thanks
Harsh S

Answer 1

Yaar I am posting my code again on this portal:
this is terrible because its not working:::
function artboardToJPGs(size)
var win = new Window("palette", "SnpCreateProgressBar", undefined, {borderless: true});
win.pnl = win.add("panel", [10, 10, 440, 100], "Creating JPEG");
win.pnl.progBar = win.pnl.add("progressbar", [20, 35, 410, 60], 0, 100);
win.pnl.progBarLabel = win.pnl.add("statictext", [20, 20, 320, 35], "0%");
        win.show ();
for(i=0; i<10; i++)
    win.pnl.progBar.value+=10;
            win.pnl.progBarLabel.text = win.pnl.progBar.value+"%";
            win.update(); 
        var idx, j, sizes, jpegOpt, doc, docName, dF, artBds, abName, scale, jpgFile, destinationFolder, originalImage;
        jpegOpt = new ExportOptionsJPEG();
        jpegOpt.Optimization = true;
        jpegOpt.QualitySetting = 100;
        jpegOpt.blurAmount=0;
        jpegOpt.artBoardClipping=false;
        dF=new Folder(jpgImageFolder);
        if ( !dF.exists ) dF.create();
        doc = app.activeDocument;
        docName=doc.name;
        artBds = doc.artboards;
        idx = artBds.getActiveArtboardIndex();
        abName = artBds[ idx ].name;
           var w= artBds[ idx ].artboardRect[2] - artBds[ idx ].artboardRect[0] ;
           var h=artBds[ idx ].artboardRect[1] - artBds[ idx ].artboardRect[3];
            var width=  100+ ( (size - w)/w ) * 100;
            var height=  100+ ( ( size - h )/h ) * 100;
            jpgFile = File( dF.fsName + '/' + fileName + size + 'x' + size + '.jpg' );
            jpegOpt.horizontalScale =width;
            jpegOpt.verticalScale = height;
            doc.exportFile( jpgFile, ExportType.JPEG ,jpegOpt );
            win.close();