Exception outside of Page Events?

I'm getting a "A first chance exception of type 'System.Web.HttpException' occurred in System.Web.dll" error after Page_Unload and I have NO idea how to figureout whats causing it...It happens after a response.write to send an xml file to the user.


            Response.Clear();
            Response.ContentType = "application/vnd.ms-excel";
            Response.AddHeader("Content-Disposition", "attachment;filename=" + outputFile);
            Response.WriteFile(reportFile);
            Response.Flush();
            Response.Close();
     &nb ...