Error while downloading pdf stored in database

Question

Getting this error:  Unable to evaluate expression because the code is optimized or a native frame is on top of the call stack.

int id = int.Parse((sender as LinkButton).CommandArgument);
       byte[] bytes;
       string fileName, contentType;
       string constr = ConfigurationManager.ConnectionStrings["JKPSC"].ConnectionString;
       try
       {
           using (SqlConnection con = new SqlConnection(constr))
           {
               using (SqlCommand cmd = new SqlCommand())
               {
                   cmd.CommandText = "select id, pdfType, pdfdata, regNo from tbl_Doc where id=@Id";
                   cmd.Parameters.AddWithValue("@Id", id);
                   cmd.Connection = con;
                   con.Open();
                   using (SqlDataReader sdr = cmd.ExecuteReader())
                   {
                       sdr.Read();
                       bytes = (byte[])sdr["pdfdata"];

                       fileName = sdr["pdfType"].ToString() + sdr["regNo"].ToString() + ".pdf";
                   }
                   con.Close();
               }
           }
           Response.Clear();
           Response.Buffer = true;
           Response.Charset = "";
           Response.Cache.SetCacheability(HttpCacheability.NoCache);
           Response.ContentType = "application/pdf";
           Response.AppendHeader("Content-Disposition", "attachment; filename=" + fileName);
           Response.BinaryWrite(bytes);
           Response.Flush();
           Response.Close();
           Response.End();


       }
       catch (Exception ex)
       {
           throw;
       }

 How to solve this error