When I use WebAnnotationViewer inside of asp:UpdatePanel, I'm getting the following error on each postback:
"Exception: 'document.frames[...]._co' is null or not an object."
Call stack (with some omissions):
atalaInitChild
atalaFireEvent
document.frames[_vp.id]._co.setZoom() <-- errors out here.

I'm wondering if you're looking into it?

Thanks, Sergey 

Environment: VS 2008, target: framework 3.5 

<form id="form1" runat="server">
<div>
<asp:ScriptManager ID="ScriptManager1" runat="server"/>
<asp:UpdatePanel ID="UpdatePanel1" runat="server">
    <ContentTemplate>
        <cc1:WebAnnotationViewer ID="WebAnnotationViewer1" runat="server"/>
        <br />
        <asp:Button ID="Button1" runat="server" Text="PostBack"/>
    </ContentTemplate>
</asp:UpdatePanel>
</div>
</form>