Data = Unable to evaluate expression because the code is optimized or a native frame is on top of the call stack.

string attachment = "attachment; filename=FormA5.pdf";
        HttpContext.Current.Response.ClearContent();
        HttpContext.Current.Response.AddHeader("content-disposition", attachment);
        HttpContext.Current.Response.ContentType = "application/pdf";
        StringWriter stw = new StringWriter();
        HtmlTextWriter htextw = new HtmlTextWriter(stw);
        Document doc = new Document(iTextSharp.text.PageSize.A4, 30, 30, 50, 50);
        //string path = Server.MapPath("PDFs");
        PdfWriter.GetInstance(doc, HttpContext.Current.Response.OutputStream);
        DataTable dt = emp.SelectEmployeeWithDesgnDeptLocComp(empid);
        doc.Open();
        Paragraph paragraphheader = new Paragraph();
        paragraphheader.SpacingAfter = 1f;
        float[] headercols = { 1f, 2f, 1.2f, 2f };
        PdfPTable table = new PdfPTable(headercols);
        table.WidthPercentage = 100f;
        PdfPCell cell = GetFormName(company);





  StringReader str = new StringReader(stw.ToString());
        HTMLWorker htmlworker = new HTMLWorker(doc);
        htmlworker.Parse(str);
        doc.Close();
        HttpContext.Current.Response.Write(doc);
        HttpContext.Current.Response.End();

//Data = Unable to evaluate expression because the code is optimized or a native frame is on top of the call stack.