Convert and format a Datarow

Question

I would like format the datas of my model thanks to a thousand separator, this datas are in a Datarow and it's not possible to use the toString() with 2 arguments (as shown in my link) on an object.

I think I must parse the Datarow to int then parse this int to a string (using toString("n", nfi)), but my code does not work.

An exception of type 'System.FormatException' occurred in mscorlib.dll but was not processed in the user code Additional information: The format of the input string is incorrect.

Example : listRow.Add(Convert.ToInt64(row["ENTITE"]).ToString("n", nfi));

Datas :

Example of datas

This is the code of my model :

                dac = new SqlDataAdapter(sql, cn);
            dsc = new DataSet();
            dac.Fill(dsc, "histo");

            List<List<string>> listHisto = new List<List<string>>();
            StringBuilder output = new StringBuilder();

            foreach (DataRow row in dsc.Tables["histo"].Rows)
            {
                CultureInfo.GetCultureInfo("fr-fr");
                NumberFormatInfo nfi = (NumberFormatInfo)
                CultureInfo.InvariantCulture.NumberFormat.Clone();
                nfi.NumberGroupSeparator = " ";

                List<string> listRow = new List<string>();

                listRow.Add(Convert.ToInt64(row["ENTITE"]).ToString("n", nfi));
                listRow.Add(Convert.ToInt64(row["M01"]).ToString("n", nfi));
                listRow.Add(Convert.ToInt64(row["M02"]).ToString("n", nfi));
                listRow.Add(Convert.ToInt64(row["M03"]).ToString("n", nfi));
                listRow.Add(Convert.ToInt64(row["M04"]).ToString("n", nfi));
                listRow.Add(Convert.ToInt64(row["M05"]).ToString("n", nfi));
                listRow.Add(Convert.ToInt64(row["M06"]).ToString("n", nfi));
                listRow.Add(Convert.ToInt64(row["M07"]).ToString("n", nfi));
                listRow.Add(Convert.ToInt64(row["M08"]).ToString("n", nfi));
                listRow.Add(Convert.ToInt64(row["M09"]).ToString("n", nfi));
                listRow.Add(Convert.ToInt64(row["M10"]).ToString("n", nfi));
                listRow.Add(Convert.ToInt64(row["M11"]).ToString("n", nfi));
                listRow.Add(Convert.ToInt64(row["M12"]).ToString("n", nfi));
                listRow.Add(Convert.ToInt64(row["TT"]).ToString("n", nfi));
                listHisto.Add(listRow);
            }

            list.Add("histo", listHisto);

            DataTable dtc = dsc.Tables["histo"];

The code of my view :

            @{
            List<List<string>> listHisto = ViewBag.ListHisto;

            bool isClassSuccess = true;
            string classLigne;

            foreach (List<string> item in listHisto)
            {
                if (isClassSuccess)
                {
                    classLigne = "class=warning";//jaune clair
                    isClassSuccess = false;
                }
                else
                {
                    classLigne = "class=success";//vert clair
                    isClassSuccess = true;
                }
                @:<tr @classLigne>
                    foreach (string row in item)
                    {
                        <td>@row</td>
                    }
                @:</tr>
            }

Thanks you in advance for your help