error during export a page to pdf in asp

Unable to cast object of type 'iTextSharp.text.html.simpleparser.IncTable' to type 'iTextSharp.text.ITextElementArra

protected void btnPDF_Click(object sender, EventArgs e)

{

Response.Clear();

Response.Buffer = true;

Response.ContentType = "application/pdf";

Response.AddHeader("content-disposition", "attachment;filename=Result.pdf");

Response.Cache.SetCacheability(HttpCacheability.NoCache);

StringWriter sw = new StringWriter();

HtmlTextWriter hw = new HtmlTextWriter(sw);

hw.AddStyleAttribute("font-size", "7pt");

hw.AddStyleAttribute("color", "Black");

pnlContents.RenderControl(hw);

StringReader sr = new StringReader(sw.ToString());

Document pdfDoc = new Document(PageSize.A4, 10f, 10f,100f,0f);

HTMLWorker htmlparser = new HTMLWorker(pdfDoc);

PdfWriter.GetInstance(pdfDoc, Response.OutputStream);

pdfDoc.Open();

htmlparser.Parse(sr);

pdfDoc.Close();

Response.Write(pdfDoc);

Response.End();