Error when wanting to pass a gridview to an excel file

You could add the EnableEventValidation="false" condition in the <% @ Page part of your page where the information is to be exported.

Try it and tell me what the result is.

Greetings.

The error comes from calling pageToRender.RenderControl(htw); , so the page generates an exception since the control is being generated outside of a form.

One solution is to avoid this exception by overwriting VerifyRenderingInServerForm this way:

public override void VerifyRenderingInServerForm(Control control)
{
}

Dear, I export in the same way that you do the data of a gridview to excel, I recommend that if you want to export everything you show in the grid and you will not modify data that is in it and only place a button to export this should be useful for you:

protected void btnExportarPendientes_Click(object sender, ImageClickEventArgs e)
{
    string nombreArchivo = "Rep_Fic_Pend_Despacho.xls";
    List<saapt010> listDatos = new List<saapt010>();
    listDatos = BuscarPendientes();
    DataGrid dg = new DataGrid();
    dg.AllowPaging = false;
    dg.DataSource = listDatos;
    dg.DataBind();

    System.Web.HttpContext.Current.Response.Clear();
    System.Web.HttpContext.Current.Response.Buffer = true;
    System.Web.HttpContext.Current.Response.ContentEncoding = Encoding.UTF8;
    System.Web.HttpContext.Current.Response.BinaryWrite(Encoding.UTF8.GetPreamble());
    System.Web.HttpContext.Current.Response.Charset = "";
    System.Web.HttpContext.Current.Response.AddHeader("Content-Disposition",
      "attachment; filename=" + nombreArchivo);

    System.Web.HttpContext.Current.Response.ContentType =
      "application/vnd.ms-excel";
    System.IO.StringWriter stringWriter = new System.IO.StringWriter();
    System.Web.UI.HtmlTextWriter htmlTextWriter =
      new System.Web.UI.HtmlTextWriter(stringWriter);
    dg.RenderControl(htmlTextWriter);
    System.Web.HttpContext.Current.Response.Write(stringWriter.ToString());
    System.Web.HttpContext.Current.Response.End();
}




protected List<saapt010> BuscarPendientes()
{
    List<saapt010> listDatos = new List<saapt010>();
    string script = String.Empty;
    string consulta = String.Empty;
    DateTime fecha = DateTime.Now;

    string conexion = ConfigurationManager.ConnectionStrings["samConnectionString"].ConnectionString;
    IfxConnection conn = new IfxConnection(conexion);
    conn.Open();
    try
    {
        consulta = ViewState["ConsultaPendientes"].ToString();
        IfxCommand cmd = new IfxCommand(consulta, conn);
        cmd.Parameters.Add("fechaUno", IfxType.DateTime).Value = Convert.ToDateTime(ViewState["FechaUnoPen"].ToString());
        cmd.Parameters.Add("fechaDos", IfxType.DateTime).Value = Convert.ToDateTime(ViewState["FechaDosPen"].ToString());
        IfxDataReader reader = cmd.ExecuteReader();

        while (reader.Read())
        {
            saapt010 saap = new saapt010();
            if (reader.GetString(1) != "")
            {
                saap.Rut = reader.GetString(1) + "-" + reader.GetString(2);
            }
            else
            {
                saap.Rut = "";
            }
            saap.Fecha = reader.GetDateTime(4).ToString("dd-MM-yyyy");
            saap.NumeroBio = reader.GetString(5);
            saap.Nombre = reader.GetString(6) + " " + reader.GetString(7) + " " + reader.GetString(8);
            saap.ServicioOrigen = reader.GetString(13);
            saap.MedicoOri = reader.GetString(14);
            saap.Prevision = reader.GetString(10);
            saap.Nmuestras = reader.GetString(12);
            if (reader.GetString(16) != "null")
            {
                saap.Supervisor = reader.GetString(16);
            }
            else
            {
                saap.Supervisor = String.Empty;
            }
            if (reader.GetString(15) != "")
            {
                fecha = Convert.ToDateTime(reader.GetString(15));
                saap.FechaDesp = fecha.ToString("dd-MM-yyyy");
            }
            else
            {
                saap.FechaDesp = String.Empty;
            }

            listDatos.Add(saap);
        }
    }
    catch (Exception ex)
    {
        script = "alert('Se ha producido un error al cambiar de página en el modulo de busqueda por pendientes de despacho. Favor comuniquese con el área de informática');";
        ClientScript.RegisterClientScriptBlock(this.GetType(), "Alert", script, true);
    }
    return listDatos;
}

If you notice, I create a variable of type List < > where I keep all the data of the grid and this is the return in the function to look for slopes that is my case. later I create a datagrid and this datagrid I assign the List < > with the data of my grid and ready. Anything you tell me and put the code to help you more.

Greetings