Cast var linq query in int issue

Question

Hi everybody, I'm trying to build a chart in asp.net. For that I'm trying to cast the result of my linq query in int type but I have an error saying that only int, string, decimal type can be use. I don't understant what happened. Is someone have an idea ?? Here is my code :

 

protected void GetChartData2()
        {
            Series series = Chart2.Series["Series2"];
            series.Color = System.Drawing.Color.Blue;

            using (Context db = new Context())
            {
                if (db.InfoLivraison.Count() > 0)
                {
                    DateTime end = Convert.ToDateTime(DateTime.Now.ToString("dd/MM/yyyy"));
                    DateTime start = end.AddDays(-7);

                    List<InfoLivraison> listCA = (from infoLivCA in db.InfoLivraison
                                                  where infoLivCA.date_command2 >= start && infoLivCA.date_command2 <= end
                                                  select infoLivCA).ToList();

                    DataTable dt2 = ToDataTable<InfoLivraison>(listCA);

                    DataTable dtjour = dt2.DefaultView.ToTable("Jours7CA", true, "date_command2");
                    DataTable dtMontant = dt2.DefaultView.ToTable("Montants7CA", true, "montantCommande");

                    if (dtjour.Rows.Count != 0)
                    {

                        for (int i = 0; i < dtjour.Rows.Count; i++)
                        {
                            DateTime selectedDate = Convert.ToDateTime(dtjour.Rows[i]["date_command2"]);
                            string selectedDateStr = Convert.ToString(selectedDate);

                            for(int j=0;j<dtjour.Rows.Count;j++)
                            {
                                var linqSum = db.InfoLivraison.GroupBy(a => selectedDate)
                                    .Select(b => new { total = b.Sum(a => Convert.ToDecimal(a.montantCommande))});

                                series.Points.AddXY(selectedDate.ToString("dd/MM/yyyy"), linqSum);
                            }
                        }
                    }
                }
            }
        }

Thanks for your help