ASP.NET 3.5: Problem exporting grid contents to word from a child page: ErrorCode=-2147467259

I am using ASP.NET 3.5 with C# code.  I have gridview by name “gridinfo” in a child page populated by records from a database.  I am using a standard function to export the grid contents to word.
private void exportgridinfotoword()

    {
       
        Response.Clear();
  Response.AddHeader("content-disposition", "inline;filename=abc.doc");
        Response.Charset = "";
        Response.Cache.SetCacheability(HttpCacheability.NoCache);
        Response.ContentType = "application/vnd.word";
        StringWriter sw = new StringWriter();
        HtmlTextWriter htw = new HtmlTextWriter(sw);
       
        gridinfo.RenderControl(htw);
        Response.Write(sw.ToString());

        Response.Flush();
        Response.End();
    }
}

I am getting the following error
Message="Control 'ctl00_Main_gridinfo' of type 'GridView' must be placed inside a form tag with runat=server." Source="System.Web"
What is the problem and likely solution