ASP.Net Error: System.Web.UI.WebControls.Panel does not contain definition for DrawToBitmap

getting following error while converting panel to image

1. System.Web.UI.WebControls.Panel does not contain definition for DrawToBitmap and no extension method DrawToBitmap 

2. The best overloaded method match for system.drawing

using (Bitmap graphicSurface = new Bitmap(pnlContents.Width, pnlContents.Height))
{
    using (StreamWriter bitmapWriter = new StreamWriter("TEST.JPEG"))
    {
        pnlContents.DrawToBitmap(graphicSurface, new Rectangle(0, 0, panel1.Width, panel1.Height));
        graphicSurface.Save(bitmapWriter.BaseStream, ImageFormat.Jpeg);
    }
}