GetCallbackEventReference doesn't do anything
<p>I have an ASP.Net application that must show a label when i changed value from a combo:</p>

<ul>
<li><p>in cs file:</p>

<pre><code> public partial class WebFormAJAXControls : System.Web.UI.Page,System.Web.UI.ICallbackEventHandler
  {
string _callbackArg;

public void RaiseCallbackEvent(string eventArgument)
{
    _callbackArg = eventArgument;
}

public string GetCallbackResult()
{
    return _callbackArg;
}

protected void Page_Load(object sender, EventArgs e)
{
    //register the name of the client side function that will be called by the server
    string callbackRef = Page.ClientScript.GetCallbackEventReference(this, "args", "ClientCallbackFunction","");

    //define a function used by client to call server
    string callbackScript = " function MyServerCall(args){alert ('1'); " + callbackRef + " ; }";

    //register the client function to the page 
    Page.ClientScript.RegisterClientScriptBlock(this.GetType(), "MyServerCall", callbackScript, true);

}
  }
</code></pre></li>
<li><p>in aspx file:</p>

<pre><code>  &lt;head runat="server"&gt;
     &lt;title&gt;&lt;/title&gt;
      &lt;script type="text/javascript"&gt;
        function ClientCallbackFunction(args) {
          alert(args);
          LabelMessage.innerText = args;
       }
     &lt;/script&gt;
  &lt;/head&gt;
  &lt;body&gt;
  &lt;form id="form1" runat="server"&gt;
   &lt;div&gt;

  &lt;asp:DropDownList ID="DropDownListChoice" runat="server" OnChanged="MyServerCall(DropDownListChoice.value)"&gt;
     &lt;asp:ListItem&gt;Choise 1&lt;/asp:ListItem&gt;
     &lt;asp:ListItem&gt;Choise 2&lt;/asp:ListItem&gt;
     &lt;asp:ListItem&gt;Choise 3&lt;/asp:ListItem&gt;
  &lt;/asp:DropDownList&gt;
  &lt;br /&gt;&lt;br /&gt;
  &lt;asp:Label ID="labelMessage" runat="server"&gt;&lt;/asp:Label&gt;
 &lt;/div&gt;
   &lt;/form&gt;
  &lt;/body&gt;
</code></pre></li>
</ul>

<p>When I  change selection in the combobox the program doesn't do anithing.Can somebody tell me what's the problem?</p>
