Error while Converting aspx page to pdf in asp .net

Error is : Extender control 'CalendarExtender1' is not a registered extender control. Extender controls must be registered using RegisterExtenderControl() before calling RegisterScriptDescriptors().Parameter name: extenderControl 

            Response.ContentType = "application/pdf";
            Response.AddHeader("content-disposition",             "attachment;filename=UserDetails.pdf");
            Response.Cache.SetCacheability(HttpCacheability.NoCache);
            StringWriter sw = new StringWriter();
            HtmlTextWriter hw = new HtmlTextWriter(sw);
from here an Exception is thrown -->  this.Page.RenderControl(hw);          
            StringReader sr = new StringReader(sw.ToString());
            Document pdfDoc = new Document(PageSize.A4, 10f, 10f, 100f, 0.0f);
            HTMLWorker htmlparser = new HTMLWorker(pdfDoc);
            PdfWriter.GetInstance(pdfDoc, Response.OutputStream);
            pdfDoc.Open();
            htmlparser.Parse(sr);
            pdfDoc.Close();
            Response.Write(pdfDoc);
            Response.End();