title: ASP.NET Custom Validator Error Message: Control referenced by the property cannot be validated
body: <p>I use ASP.NET and have a Button and a CustomValidator, which has to validate
  the button.</p>
  
  <pre><code>&lt;asp:Button ID="saveButton" runat="server" OnClick="SaveButton_Click" Text="Speichern"
      CausesValidation="true"/&gt;
  &lt;asp:CustomValidator runat="server" ID="saveCValidator" Display="Static"
      OnServerValidate="EditPriceCValidator_ServerValidate"   
      ControlToValidate="saveButton" ErrorMessage=""&gt;
  </code></pre>
  
  <p>When loading the page, I receive the error message:</p>
  
  <blockquote>
    <p>"Control 'saveButton' referenced by
    the ControlToValidate property of
    'saveCValidator' cannot be validated."</p>
  </blockquote>
  
  <p>What might be the problem? I searched on the net, but this didn´t help much.</p>