title: Sys.InvalidOperationException: Handler must be a function
body: <p>I've a webpage which contains a TabContainer</p>
  
  <pre><code>&lt;%@ Register Assembly="AjaxControlToolkit" Namespace="AjaxControlToolkit" TagPrefix="cc1" %&gt;
  ...
  ....
  &lt;form id="form1" runat="server"&gt;
      &lt;asp:ScriptManager ID="sm1" runat="server"&gt;&lt;/asp:ScriptManager&gt;
      &lt;cc1:TabContainer runat="server" ID="tbcTabContainer" OnClientActiveTabChanged="ChangeTab()"&gt;&lt;/cc1:TabContainer&gt;
  &lt;/form&gt;
  </code></pre>
  
  <p>which calls a js function which at the moment does nothing.</p>
  
  <pre><code>&lt;script  type="text/javascript"&gt;
  function ChangeTab()
  {
      alert('Sucesss');
  }
  &lt;/script&gt;
  </code></pre>
  
  <p>In my page load in the code behind I create a couple of tab panels and add them to the container. Now, my problem is that when i change tab, the javascript alert box shows but once i close it i get the error</p>
  
  <p>Microsoft JScript runtime error: Sys.InvalidOperationException: Handler must be a function.</p>