How to Render Panel Control in Asp.net

First Of All //
EnableEventValidation="false"
use this line in fisrt line of designe window

protected void ImageButton1_Click(object sender, ImageClickEventArgs e)
{
StringWriter swriter = new StringWriter();
HtmlTextWriter twrite = new HtmlTextWriter(swriter);
this.MainPanel.RenderControl(twrite);
string text = swriter.ToString();
}
public override void VerifyRenderingInServerForm(Control control)
{
}