Cast var linq query in int issue

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 listCA = (from infoLivCA in db.InfoLivraison
where infoLivCA.date_command2 >= start && infoLivCA.date_command2 <= end
select infoLivCA).ToList();
DataTable dt2 = ToDataTable(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
{
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