title: ASPxClientComboBox AddItem method throws an error
body: <p>When calling <code>ASPxClientComboBox.AddItem()</code> I get an error in the <code>_aspxRemoveAttribute</code> function, that obj is null.</p>
  
  <p>I've traced it to the <code>CreateNewItem</code> function, which never returns a result.</p>
  
  <p>My combo box starts unpopulated, and I'm trying to add items on the client side, but I got the same error when trying to add items to a combo box with items already added from the server side.</p>
  
  <p>This is using the v2011 vol 2.5 release.</p>
  
  <p><strong>EDIT</strong>
  Here is the combo box markup:</p>
  
  <pre><code>&lt;dx:ASPxComboBox ID="txtCountry" runat="server" Width="95%" data-bind="dxDataBind: Countries, keyMember: 'Id', displayMember: 'Name', SelectedKey: CountryId"&gt;
      &lt;ValidationSettings&gt;
          &lt;RequiredField IsRequired="True" ErrorText="Country required" /&gt;
      &lt;/ValidationSettings&gt;
  &lt;/dx:ASPxComboBox&gt;
  </code></pre>
  
  <p>The data-bind attribute is part of KnockoutJS, which I am attempting to adapt to bind to other controls.</p>
  
  <p>Essentially at the moment I'm just trying to add an item to an empty combo box on the client side, with two string parameters.</p>