Cannot get TabStrip Object on the Clientside

[Christian]

Hi,
I have got an radtabstrip in combination with radpageview on my page. I got 2 tabs and 2 pageviews. Now I am trying to disable one of the two tabs on the clientside. But I don't get the real clientside Object and so cannot call the findTab ... functions.
I always get an object of the type: DispHTMLDivElement.

What I am doing wrong?

<telerik:radsplitter runat="server" id="splitter2" orientation="Horizontal">
                        <telerik:radpane id="panel2a" runat="server" scrolling="None" borderstyle="none" borderwidth="0" height="26">
                            <telerik:radtabstrip  runat="server" causesvalidation="false" skin="Vista" id="tabStripHistory" multipageid="multiPage1"
                                selectedindex="0"  style="margin-top:2px">
                                <tabs>
                                    <telerik:radtab text="Page1" pageviewid="pagaViewId1" value="a">
                                    </telerik:radtab>
                                    <telerik:radtab text="Page2" pageviewid="pagaViewId2" value="b">
                                    </telerik:radtab>
                                </tabs>
                            </telerik:radtabstrip>
                        </telerik:radpane>
                        <telerik:radpane runat="server" id="panel2b" scrolling="Both" borderstyle="none" borderwidth="0">
                            <telerik:radmultipage runat="server" id="multiPage1" selectedindex="0" width="100%">
                                <telerik:radpageview runat="server" id="pagaViewId1">
                                    <telerik:radtreeview .../>
                                </telerik:radpageview>
                                <telerik:radpageview runat="server" id="pagaViewId2">

                                    <asp:panel ...