Object Reference Not Set Error on RenderControl() method

[eromurugan]

Hi, I have web page with multiple Chart FX 7.0 Controls in it. I want to export all the content in a container like Panel to excel. Panel contains the charts. I am using the following code to achieve it.

string exportContent = string.Empty;

HttpResponse response = CreateExcelFile(fileName);using (StringWriter sw = new StringWriter()) {

using (HtmlTextWriter htw = new HtmlTextWriter(sw)) {HtmlTable t = new HtmlTable();

HtmlTableRow top = new HtmlTableRow();HtmlTableCell tcell = new HtmlTableCell();

tcell.Controls.Add(control);

top.Cells.Add(tcell);

t.Rows.Add(top);

t.RenderControl(htw);

HttpContext.Current.Response.Write(sw.ToString());HttpContext.Current.Response.End();

} }

I am getting error Object Reference not set at line t.RenderControl(htw);

Please help me. 

Thanks in advance.