GridView row Updating event not firing in ASP.Net

i m using ajax datetimepicker on this page. in gridview autogenerate row updating event not fire.

<asp:GridView ID="grdexpense" runat="server" AutoGenerateDeleteButton="True" Width="100%" AutoGenerateEditButton="True" OnRowCancelingEdit="grdexpense_RowCancelingEdit" OnRowDeleting="grdexpense_RowDeleting" OnRowEditing="grdexpense_RowEditing" OnRowUpdating="grdexpense_RowUpdating" AutoGenerateColumns="True" ViewStateMode="Disabled" DataKeyNames="id,Expense_Type,Month_Year" BackColor="White" BorderColor="#C0D23C" BorderWidth="2px" GridLines="Both">
        <AlternatingRowStyle BackColor="White" />
</asp:GridView>

    protected void grdexpense_RowUpdating(object sender, GridViewUpdateEventArgs e)
    {
        GridViewRow row = grdexpense.Rows[e.RowIndex];
       // string columncount = grdexpense.Rows[0].Cells.Count.ToString();

        string id = grdexpense.DataKeys[e.RowIndex].Values[0].ToString();
        string expensetype = grdexpense.DataKeys[row.RowIndex].Values[1].ToString();
        string month_year = grdexpense.DataKeys[row.RowIndex].Values[2].ToString();
        string head_id = bsql.getsinglevallue("select expanse_head_id from headvise_expenses where id='" + id + "'");
    }