UpdatePanel doesn't refresh a Grid

Hi guys,

I have a Grid in an UpdatePanel with a trigger to a button. But it doesn't refresh the data when I click to the button. I have conditional UpdateMode, and i call a UpdatePanel5.Update() when I want to refresh, but it doesn't work :S

<td style="width:28%;" align= "left">
<asp:ImageButton ID="BtnBuscarTit" runat="server" OnClick="lnkBuscarTitulares" ImageUrl="~/web/Images/btn_buscar.GIF"/>
</td>

<asp:UpdatePanel ID="UpdatePanel5" runat="server" UpdateMode="conditional">
<Triggers>
<asp:AsyncPostBackTrigger ControlID="BtnBuscarTit" EventName="Click" />
</Triggers>
<ContentTemplate>
<asp:GridView ID="RejillaTitularesExp"

...

</asp:UpdatePanel>

Any idea? Regards