title: ControlID could not be found for AsyncPostBackTrigger
body: <pre><code>  &lt;asp:UpdatePanel ID="CartUpdatePanel" runat="server"&gt;
          &lt;Triggers&gt;
              &lt;asp:AsyncPostBackTrigger ControlID='&lt;%= rdoSelect.ClientID %&gt;'/&gt;
          &lt;/Triggers&gt;
          &lt;ContentTemplate&gt;
              &lt;asp:Timer ID="cartTimer" Interval="5000" runat="server" OnTick="cartTimer_Tick"&gt;
              &lt;/asp:Timer&gt;
              &lt;asp:GridView ID="gridCartSearch" runat="server" AutoGenerateColumns="False"&gt;
                  &lt;Columns&gt;
                      &lt;asp:TemplateField HeaderText="Select"&gt;
                          &lt;ItemTemplate&gt;
  
                              &lt;asp:HiddenField ID="Serial" runat="server" Value='&lt;%# Eval("serialnum") %&gt;' /&gt;
                              &lt;asp:RadioButton ID="rdoSelect" runat="server" AutoPostBack="true" GroupName="radioBtns"
                                  OnCheckedChanged="rdoSelect_CheckedChanged" /&gt;
                          &lt;/ItemTemplate&gt;
                      &lt;/asp:TemplateField&gt;
  
                  &lt;/Columns&gt;
              &lt;/asp:GridView&gt;
          &lt;/ContentTemplate&gt;
      &lt;/asp:UpdatePanel&gt;
  </code></pre>
  
  <p>I'm getting the following error</p>
  
  <blockquote>
    <p>A control with ID '&lt;%=
    rdoSelect.ClientID %>' could not be
    found for the trigger in UpdatePanel
    'CartUpdatePanel'.</p>
  </blockquote>