UpdatePanel and GridView button paging

Hi,

I have a gridview in a visual webpart. This gridview is periodically refreshed every second.To do that, I used an updatepanel and a timer as follows:

<asp:UpdatePanel ID="UpdatePanel1" runat="server"><ContentTemplate><asp:Timer ID="Timer1" runat="server" Interval="1000" ontick="Timer1_Tick"></asp:Timer><asp:GridView ID="GridView1" runat="server"  PageSize="10" OnPageIndexChanging="gridView_PageIndexChanging" AllowPaging="True"
                EmptyDataText = "Pas d'enregistrements à afficher"><PagerSettings Mode="NextPrevious" NextPageImageUrl="~/_layouts/images/ServiceDirect/suiv.png"
                    PreviousPageImageUrl="~/_layouts/images/ServiceDirect/pred.png" /><Columns><asp:BoundField DataField="IDIncident" HeaderText="ID demande"
            SortExpression="IDIncident" HeaderStyle-Width="100" /><asp:BoundField DataField="Date" HeaderText="Date début"
            SortExpression="DateD" HeaderStyle-Width="220" /><asp:BoundField DataField="TRC" HeaderText="TRC (En heures)"
            SortExpression="TRC" /><asp:BoundField DataField="DateF" HeaderText="Date fin"
            SortExpression="DateF" HeaderStyle-Width="220"  /></Columns></asp:GridView></ContentTemplate></asp:UpdatePanel>

My problem is that after using the updatepanel, the button paging gridview does not work anymore (don't do postback). Have you any idea how to Resolve this problem?