Update panel can not find the button which trigger it

I have a button is inside a another table(s) inside the update panel.

<Update panel>
<ContentTemplate>
<table>
  <table>
    <Button>
 <table>
<table>
</ContentTemplate>
</Update panel>

I would like to add a button to Update panel's trigger. But am getting an err says "Update panel can not find the button which trigger it".

I am getting "Sys.Webforms.PageRequestmanagerParseErrorException: This message recieved from manager could not be parsed.开发者_C百科 Common cause for this error are when response is modified by response.write"

Please help!

PostBackTrigger example:

<asp:ScriptManager ID="ScriptManager1" runat="server"></asp:ScriptManager>

<asp:UpdatePanel ID="UpdatePanel1" runat="server">
 <ContentTemplate>
  <asp:Button ID="btn1" runat="server" Text="Button 1-Partial Postback" />
  <asp:Button ID="btn2" runat="server" Text="Button 2-Full Postback" />
 </ContentTemplate>
 <Triggers>
  <asp:PostBackTrigger ControlID="btn2" />
 </Triggers>
</asp:UpdatePanel>