I have a TreeView in a UserControl with a large number of nodes which I am displaying in a popup using ModalPopupExtender.  However it significantly slows down its host page on load while the TreeView is being populated.

 Here is a snippit of the code on the host page:

    <cc1:ModalPopupExtender ID="ContainerPopupExtender" runat="server" BackgroundCssClass="modalBackground"
        CancelControlID="btnContainerClose" OkControlID="btnContainerOk" PopupControlID="pnlContainer"
        TargetControlID="cAddContainerBtn" >
    </cc1:ModalPopupExtender>

     <asp:Panel ID="pnlContainer" runat="server"  Style="display: none">
        <uc2:ContainerSelection ID="ucContainerSelection" runat="server" />
        <div style="modalControls">
            <asp:Button ID="btnContainerOk" runat="server" Text="OK" Style="display: none" />
            <asp:Button ID="btnContainerClose" runat="server" Text="Close" />
        </div>    
    </asp:Panel>  

 And here is the ContainerSelection aspx: 

<asp:Panel ID="pnlContainerUserControl" runat="server" >
    <asp:Label ID="lblTitle" runat="server" Text="Select a container"></asp:Label>
    <asp:TreeView ID="tvContainers" runat="server" OnSelectedNodeChanged="tvContainers_SelectedNodeChanged">
    </asp:TreeView>
</asp:Panel>

I tried to use a method described by Joshua Stengel on CodeProject which uses an asp:Timer to postpone the loading of the TreeView content by enclosing it in an UpdatePanel. It all appeared to work fine until I tried to select one of the nodes, at which point I get a JavaScript error 'ct00_DefaultContent_ucContainerSelection_tvContainers_Data' is undefined'.

 After some googling about ModalPopupExtender, UpdatePanel and TreeView's I find out that the TreeView control isn't compatible with an UpdatePanel (however I've seen some sample code where this is the case).

Is it possible to do the above ?

Are there any other solutions to delay the loading of a TreeView in this scenario ? 

Some background info:

• The number of root nodes in the TreeView is significant, so only loading a node when its expanded (e.g. using a web service) isn't going to help.
• I'm using ASP.NET 2.0
• The web application uses master pages. 
• The TreeView content won't change while its displayed, so loading up the whole hierarchy on the initial load is acceptable.
• All I need to do is select a single node.

Any help would be appreciated.

Kitog.