Problem with Crystal Report in ASP.NET - ExportToHttpResponse

Question

I am using the code to export pdf file from a popup.

On button click

  function popupReport() 
    {
        var url = 'Report.aspx';
        window.open(url, 'winPopupReport', 'width=300,height=300,resizable=no,scrollbars=no,toolbar=no,directories=no,status=no,menubar=no,copyhistory=no');
        return false;
    }

and in Report.aspx.cs

 ReportDocument repDoc = ( ReportDocument ) System.Web.HttpContext.Current.Session["StudyReportCrystalDocument"];
        // Stop buffering the response
        Response.Buffer = false;
        // Clear the response content and headers
        Response.ClearContent();
        Response.ClearHeaders();
        try
        {
            repDoc.ExportToHttpResponse( CrystalDecisions.Shared.ExportFormatType.PortableDocFormat, Response, true, "StudyReport" );
        }
        catch( Exception ex )
        {
        }

The code works fine in IE7. But in IE6 the popup window is not closing. Why this happends?