title: Form validation with "checkbox accept terms condition" field in C# (server side check)
body: <p>I need to show an asterix to the correspondent checkbox when the user try to send the form without check the checkbox...
  I found something like this but is not working, like the normal others <code>&lt;asp:RequiredFieldValidator</code> fields:</p>
  
  <pre><code>&lt;asp:CustomValidator  ID="CheckBoxValidator" runat="server" onservervalidate="CheckBoxRequired_ServerValidate" Display="Dynamic" CssClass="error-text" ErrorMessage='*' ValidationGroup="save"&gt; * &lt;/asp:CustomValidator&gt;
  </code></pre>
  
  <p>asp:CheckBox ID="YourCheckBox" runat="server" text=" I accept your terms and conditions bla bla bla" /></p>
  
  <p>And in the code behind I have:</p>
  
  <pre><code>protected void CheckBoxRequired_ServerValidate(object sender, ServerValidateEventArgs e)
  {
    e.IsValid = YourCheckBox.Checked;
    labelMessage.Text = "Your reservation has been processed."; 
  }
  </code></pre>