Problemino griglia c# e ms excel

Lavorando su di un progetto abbastanza complesso mi sono scrontrato con un problemino sulla visualizzazione di griglie di dati su di un foglio MS Excel.
Dovevo inserire assolutamente questo primo metodo, altrimenti non andava proprio!
Ambiente: MS VS 2005 .net 2.0 aspx

/// <summary>
/// Questo metodo deve essere presente per un bug del framework .net 2.0
/// </summary>
/// <param name="control"></param>
public override void VerifyRenderingInServerForm(Control control)
{
return;
}


Poi ho tranquillamente popolato il foglio excel con la griglia di dati.

protected void Export_Click(object sender, EventArgs e)
{
try
{
Button button = (Button)sender;
HiddenField fieldId = (HiddenField)button.Parent.Parent.FindControl("Field_Id");

string yearMonth = fieldId.Value;
int lastDayMonth = DateTime.DaysInMonth(Convert.ToInt16(yearMonth.Substring(0, 4)), Convert.ToInt16(yearMonth.Substring(4, 2)));
StringWriter stringWrite = new StringWriter();
HtmlTextWriter htmlTextWriter = new HtmlTextWriter(stringWrite);

htmlTextWriter.WriteLine("TITOLO DI ESEMPIO");
htmlTextWriter.WriteBreak();
htmlTextWriter.WriteBreak();
htmlTextWriter.WriteFullBeginTag("table border='1'");
htmlTextWriter.WriteFullBeginTag("tr");
htmlTextWriter.WriteFullBeginTag("td bgcolor='#BFCEEE' align='left'");
htmlTextWriter.WriteLine(" " + ConvertyearMonth(yearMonth));
htmlTextWriter.WriteEndTag("td");
htmlTextWriter.WriteEndTag("tr");
htmlTextWriter.WriteFullBeginTag("tr");
htmlTextWriter.WriteFullBeginTag("td");

GridView gridView = (GridView)button.Parent.Parent.FindControl("GridView1");
gridView.HeaderStyle.ForeColor = Color.Black;
gridView.RowStyle.ForeColor = Color.Black;
gridView.BorderWidth = Unit.Pixel(1);
int numRows = gridView.Rows.Count;

for (int i = 1; i < 32; i++)
{
if (i <= lastDayMonth)
{
if (Utility.Holiday(yearMonth.Substring(0, 4), yearMonth.Substring(4, 2), Convert.ToString(i)))
{
gridView.Columns[i+1 ].HeaderStyle.BackColor = Color.FromArgb(255, 119, 112);
gridView.Columns[i+1 ].HeaderStyle.ForeColor = Color.Black;
for (int j = 0; j < numRows; j++)
{
gridView.Rows[j].Cells[i+1 ].BackColor = Color.FromArgb(255, 119, 112);
}
}
}
}

gridView.RenderControl(htmlTextWriter);

htmlTextWriter.WriteEndTag("td");
htmlTextWriter.WriteEndTag("tr");
htmlTextWriter.WriteEndTag("table");

htmlTextWriter.WriteBreak();
htmlTextWriter.WriteFullBeginTag("table border='1'");
htmlTextWriter.WriteFullBeginTag("tr");
htmlTextWriter.WriteFullBeginTag("td");

GridView gridView2 = (GridView)button.Parent.Parent.FindControl("GridView2");
gridView.HeaderStyle.ForeColor = Color.Black;
gridView2.HeaderStyle.Height = Unit.Pixel(0);
gridView2.RowStyle.ForeColor = Color.Black;
gridView2.Width = Unit.Pixel(300);
gridView2.BorderWidth = Unit.Pixel(1);
gridView2.RenderControl(htmlTextWriter);

htmlTextWriter.WriteEndTag("td");
htmlTextWriter.WriteEndTag("tr");
htmlTextWriter.WriteEndTag("table");

HttpResponse response = HttpContext.Current.Response;
response.Clear();
response.Charset = "";
response.Buffer = true;
response.AddHeader("content-disposition", "attachment; filename=esempio.xls");
response.ContentType = "application/vnd.ms-excel";
response.Write(stringWrite.ToString());
response.End();
}
catch (Exception ex)
{
log.Error(ex);
}

}