title: No error message displayed for custom validator
body: <p>I have a requirement that one of multiple fields is required.  Using custom validator the even fires, false is returned, but no error message is display and the form validates.  </p>
  
  <p>What am I missing?  I have tried with and without ValidationSummary.</p>
  
  <p>Thanks!</p>
  
  <pre><code>&lt;asp:CustomValidator ID="CustomValidator1" OnServerValidate="validatePhone" EnableClientScript="false" runat="server" ErrorMessage="Home or Cell Phone is Required" &gt;&lt;/asp:CustomValidator&gt;
  
  &lt;asp:ValidationSummary ID="ValidationSummary1" DisplayMode="BulletList"  runat="server" ForeColor="Red" Font-Size="X-Small" Font-Bold="true" /&gt;
  
  
  protected void validatePhone(object sender, ServerValidateEventArgs e)
      {
          e.IsValid = string.IsNullOrEmpty(txtCellPhone.Text) &amp;&amp; string.IsNullOrEmpty(txtHomePhone.Text) ? false : true;
      }
  </code></pre>