title: Dropdownlist does not trigger the SelectedIndexChanged
body: <p>I have a dropdownlist (dr1) that is supposed to trigger the update of dr2 without affecting dr3. The problem is that dr1 triggers the update, but does not go into dr1_SelectedIndexChanged. I know that because the label does not change and that the pause does not happen</p>
  
  <p>Here is my HTML code:</p>
  
  <pre><code>&lt;form runat="server"&gt;
  &lt;asp:ScriptManager ID="sm" runat="server" /&gt;
  &lt;asp:UpdateProgress ID="UpdateProgress1" runat="server" DisplayAfter="5"&gt;
      &lt;ProgressTemplate&gt;
          &lt;span style="color: Red"&gt;Updating.....&lt;/span&gt;
      &lt;/ProgressTemplate&gt;
  &lt;/asp:UpdateProgress&gt;
  &lt;asp:DropDownList ID="dr1" AutoPostBack="true" OnSelectedIndexChanged="dr1_SelectedIndexChanged" runat="server" /&gt;
  &lt;asp:UpdatePanel ID="updpnl" runat="server"&gt;
      &lt;ContentTemplate&gt;
          &lt;asp:DropDownList ID="dr2" runat="server" /&gt;
          &lt;asp:Label ID="lbl" runat="server" /&gt;
      &lt;/ContentTemplate&gt;
      &lt;Triggers&gt;
          &lt;asp:AsyncPostBackTrigger ControlID="dr1" EventName="SelectedIndexChanged" /&gt;
      &lt;/Triggers&gt;
  &lt;/asp:UpdatePanel&gt;
  &lt;asp:DropDownList ID="dr3" runat="server" /&gt;
  &lt;/form&gt;
  </code></pre>
  
  <p>and my codebehind:</p>
  
  <pre><code>void Page_Load()
          {
              if (!IsPostBack)
              {
                  java.Text = "&lt;script language=\"JavaScript1.2\" type=\"text/javascript\"&gt;var sess = \"" + Session["username"] + "\";var user = \"" + Request.ServerVariables["LOGON_USER"].Replace("\\", "\\\\") + "\";&lt;/script&gt;";
                  dr1.Items.Clear();
                  dr2.Items.Clear();
                  dr3.Items.Clear();
                  dr1.Items.Add("");
                  dr1.Items.Add("A");
                  dr1.Items.Add("B");
                  dr1.Items.Add("C");
                  dr1.Items.Add("D");
                  dr3.Items.Add("");
                  dr3.Items.Add("Allo");
                  dr3.Items.Add("Bonjour");
                  dr3.Items.Add("Ola");
              }
          }
  
          protected void dr1_SelectedIndexChanged(Object sender, EventArgs e)
          {
              System.Threading.Thread.Sleep(5000);
              lbl.Text = DateTime.Now.ToString();
              dr2.Items.Clear();
              dr2.Items.Add("");
              for (int i = 1; i &lt;= 4; i++)
                  dr2.Items.Add(dr1.SelectedValue + i);
          }
  </code></pre>
  
  <p>I hope that someone can help me</p>
  
  <p>Thank you</p>