title: Update Panel Not working For Checkbox
body: <p>In the below code Changing <strong>asyncPostBackTrigger</strong> to <strong>PostBackTrigger</strong> causing the entirepage postback.  </p>
  
  <p>But the below code is not at all doing anything when we use the trigger as <strong>asyncPostBackTrigger</strong>.</p>
  
  <p>Any suggestions about what I am doing wrong??</p>
  
  <pre><code>&lt;%@ Page Language="VB" AutoEventWireup="false" CodeFile="Default.aspx.vb" Inherits="_Default" %&gt;
  
  &lt;!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"&gt;
  
  &lt;html xmlns="http://www.w3.org/1999/xhtml"&gt;
  &lt;head runat="server"&gt;
      &lt;title&gt;&lt;/title&gt;
  &lt;/head&gt;
  &lt;body&gt;
      &lt;form id="form1" runat="server"&gt;
          &lt;asp:ScriptManager ID="ScriptManager1" runat="server" /&gt;
              &lt;asp:UpdatePanel runat="server" ID="UpdatePanel_1" &gt;
  
                  &lt;ContentTemplate&gt;
                      &lt;asp:CheckBox ID="chkNotKnown" runat="server" AutoPostBack="True" 
                                      Text="(Not Known)" OnCheckedChanged="chkNotKnown_CheckedChanged"/&gt;
                  &lt;/ContentTemplate&gt;
  
                  &lt;Triggers&gt;
                      &lt;asp:asyncPostBackTrigger ControlID="chkNotKnown"/&gt;
                  &lt;/Triggers&gt;
  
              &lt;/asp:UpdatePanel&gt;
  
          &lt;asp:TextBox ID="txtDrCode" runat="server" OnFocus="this.style.borderColor='red'" OnBlur="this.style.borderColor=''"&gt;&lt;/asp:TextBox&gt;
      &lt;/form&gt;
  &lt;/body&gt;
  
  &lt;/html&gt;
  </code></pre>
  
  <hr>
  
  <pre><code>Partial Class _Default
      Inherits System.Web.UI.Page
      Protected Sub chkNotKnown_CheckedChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles chkNotKnown.CheckedChanged
          With txtDrCode
              If chkNotKnown.Checked Then
                  .Text = "Not Known"
                  .Enabled = False
              Else
                  .Text = ""
                  .Enabled = True
              End If
          End With
      End Sub
  End Class
  </code></pre>