zapisanie DataTable do Excela

 DataTable dt ;//zapełnią danymi z zapytania sql

saveFileDialog2.Filter = "Skoroszyt programu Microsoft Office Excel |*.xls";
saveFileDialog2.Title = "Zapisz do Microsoft Office Excel - plik xls";
saveFileDialog2.FileName = nazwa + ".xls";
if (saveFileDialog2.ShowDialog() == System.Windows.Forms.DialogResult.OK)
{
       string path = saveFileDialog2.FileName;         
}

        private void zapis_scv(DataTable dt, OleDbDataAdapter DataAdapter)
        {
            DataSet ds = new DataSet("New_DataSet");
            string nazwa = dt.Rows[0][1].ToString() +"_"+ dt.Rows[0][2].ToString();
            string nazwa2 = "";
            foreach (char x in nazwa)
            {
                if (x == ' ' || x == '/' || x == '\\' || x == '?' || x == '*' || x == '"' || x == '<' || x == '>' || x == '|' || x == ':')
                {
                    nazwa2 = nazwa2 + "_";
                }
                else
                {
                    nazwa2 = nazwa2 + x;
                }
            }
            nazwa = nazwa2;
            dt.Columns.Remove("a");
            ds.Tables.Clear();
            ds.Tables.Add(dt);

            if (checkBox2.Checked == true) // scv - CSV
            {
                saveFileDialog1.Filter = "CSV |*.csv";
                saveFileDialog1.Title = "Zapisz do pliku CSV";
                saveFileDialog1.FileName = nazwa+".csv";
                if (saveFileDialog1.ShowDialog() == System.Windows.Forms.DialogResult.OK)
                {
                        string path = saveFileDialog1.FileName;
                        StreamWriter sw = new StreamWriter(path,false,Encoding.UTF8);
                        sw.Write(ToCsv(dt));
                        sw.Dispose();
                } 
            }
            if (checkBox1.Checked == true) //excel
            {
                
                saveFileDialog2.Filter = "Skoroszyt programu Microsoft Office Excel |*.xls";
                saveFileDialog2.Title = "Zapisz do Microsoft Office Excel - plik xls";
                saveFileDialog2.FileName = nazwa + ".xls";
                
                if (saveFileDialog2.ShowDialog() == System.Windows.Forms.DialogResult.OK)
                {
                    string path = saveFileDialog2.FileName;
                    ExcelLibrary.DataSetHelper.CreateWorkbook(path, ds);
                    saveFileDialog2.Dispose();                  
                }
            }

<table>
	<tr>
		<th>Pierwszy rekord</th>
		<th>Druga komórka</th>
	</tr>
	<tr>
		<td>drugi wiersz</td>
		<td>2.2</td>
	</tr>
	<tr>
		<td colspan="2">połączone</td>
	</tr>
	<tr>
		<td rowspan="2">w pionie</td>
	</tr>
	<tr>
		<td>połączone</td>
	</tr>
</table>

public static string ConvertDataTableToHtml(DataTable targetTable)
        {
            string htmlString = "";

            if (targetTable == null)
            {
                throw new System.ArgumentNullException("targetTable");
            }

            StringBuilder htmlBuilder = new StringBuilder();

            //Create Top Portion of HTML Document
            htmlBuilder.Append("<table border='1px' cellpadding='5' cellspacing='0' ");
            htmlBuilder.Append("style='border: solid 1px Black; font-size: small;'>");

            //Create Header Row
            htmlBuilder.Append("<tr align='left' valign='top'>");

            foreach (DataColumn targetColumn in targetTable.Columns)
            {
                htmlBuilder.Append("<td align='left' valign='top'>");
                htmlBuilder.Append(targetColumn.ColumnName);
                htmlBuilder.Append("</td>");
            }

            htmlBuilder.Append("</tr>");

            //Create Data Rows
            foreach (DataRow myRow in targetTable.Rows)
            {
                htmlBuilder.Append("<tr align='left' valign='top'>");

                foreach (DataColumn targetColumn in targetTable.Columns)
                {
                    htmlBuilder.Append("<td align='left' valign='top'>");
                    htmlBuilder.Append(myRow[targetColumn.ColumnName].ToString());
                    htmlBuilder.Append("</td>");
                }

                htmlBuilder.Append("</tr>");
            }

            //Create Bottom Portion of HTML Document
            htmlBuilder.Append("</table>");

            //Create String to be Returned
            htmlString = htmlBuilder.ToString();

            return htmlString;
        }

                saveFileDialog2.Filter = "Skoroszyt programu Microsoft Office Excel |*.xls";
                saveFileDialog2.Title = "Zapisz do Microsoft Office Excel - plik xls";
                saveFileDialog2.FileName = nazwa + ".xls";
                
                if (saveFileDialog2.ShowDialog() == System.Windows.Forms.DialogResult.OK)
                {
                    string path = saveFileDialog2.FileName;
                    //Excel.Workbook book = new Excel.Workbook();
                    //Excel.Worksheet worksheet = new Excel.Worksheet();
                    //book.Worksheets.Add(worksheet);
                    //ExcelLibrary.DataSetHelper.CreateWorkbook(path, ds);
                    // double test = Convert.ToDouble(path.Length);
                    // label12.Text = test.ToString();
                    //saveFileDialog2.Dispose();
                    StreamWriter sw = new StreamWriter(path, false, Encoding.UTF8);
                    sw.Write(ConvertDataTableToHtml(dt));
                    sw.Dispose();

            htmlBuilder.Append("<table border='1px' cellpadding='5' cellspacing='0' ");
            htmlBuilder.Append("style='border: solid 1px Black; font-size: small;'>");