Gridview not refreshing data

<asp:GridView ID="gridPedido" runat="server" CssClass="miGrid" AutoGenerateColumns="false" DataKeyNames="CodProducto,Variante"
            onrowdeleting="gridPedido_RowDeleting" onrowcommand="gridPedido_RowCommand" OnSelectedIndexChanged="gridPedido_SelectedIndexChanged"  >
                <Columns>
                    <asp:BoundField DataField="Pedido" HeaderText="Pedido" HeaderStyle-HorizontalAlign="Left" ItemStyle-HorizontalAlign="Left" ReadOnly="true" />
                    <asp:BoundField DataField="Linea" HeaderText="Linea" ItemStyle-HorizontalAlign="Left" ReadOnly="true" />
                    <asp:BoundField DataField="CodProducto" HeaderText="Tipo Contenedor" />
                    <asp:BoundField DataField="Producto" HeaderText="Tipo" ItemStyle-HorizontalAlign="Left" ReadOnly="true" />
                    <asp:BoundField DataField="Variante" HeaderText="Variante" ItemStyle-HorizontalAlign="Center" ReadOnly="true"  />
                    <asp:BoundField DataField="Servicio" HeaderText="Servicio" ItemStyle-HorizontalAlign="Center" ReadOnly="true" />
                    <asp:CommandField ShowEditButton="false" EditText="Editar" UpdateText="Aceptar"
                    CancelText="Cancelar" DeleteText="Borrar" ButtonType="Image"
                    CancelImageUrl="~/resources/images/cancelar.png" EditImageUrl="~/resources/images/modificar.png"
                        ShowSelectButton="true" SelectText="Seleccionar" SelectImageUrl="~/resources/images/modificar.png"
                    UpdateImageUrl="~/resources/images/aceptar.png" ShowDeleteButton="true"  DeleteImageUrl ="~/resources/images/basura.png"/>
                    <asp:ButtonField Text="Añadir contenido" ImageUrl="~/resources/images/add.png" CommandName="AñadirContenido" ButtonType="Image" />
                </Columns>
                <EmptyDataTemplate>
                <div style="text-align:center">No se han encontrado elementos</div>
                </EmptyDataTemplate>
            </asp:GridView>

protected void ActualizarGrid()
{
    DataTable dtlineas = f.ObtenerLineasPedidoWeb(Session["Pedido"].ToString());
    ViewState["Lineas"] = dtlineas;

    gridPedido.DataSource = null;
    gridPedido.DataBind();
    gridPedido.DataSource = dtlineas;
    gridPedido.DataBind();

    if (gridPedido.Rows.Count > 0)
    {
        pnl_Pedido.Visible = true;
    }
}