title: UpdatePanel or RadAjaxPanel in RadGrid EditForm template not working
body: <p>I have a RadGrid in which I'm using an EditForm FormTemplate.</p>
  
  <p>Inside of this there's a list (RadComboBox) with some companies. When a user selects one of these companies, it should fill another RadComboBox with a list of all locations.</p>
  
  <p>At first I tried this using an UpdatePanel, then a RadAjaxPanel. Neither work.</p>
  
  <p>This is a stripped down version:</p>
  
  <pre><code>&lt;FormTemplate&gt;
      &lt;table&gt;
          &lt;telerik:RadAjaxPanel runat="server"&gt;
              &lt;tr&gt;
                  &lt;td&gt;
                      Company
                  &lt;/td&gt;
                  &lt;td&gt;
                      &lt;telerik:RadComboBox ID="rcbCompany" runat="server" Width="250px" ValidationGroup="NewResource"
                          DataTextField="C_Name" DataValueField="Bedrijf_ID" AppendDataBoundItems="true"
                          OnSelectedIndexChanged="rcbCompany_OnSelectedIndexChanged"&gt;
                      &lt;/telerik:RadComboBox&gt;
                  &lt;/td&gt;
              &lt;/tr&gt;
              &lt;tr&gt;
                  &lt;td&gt;
                      Locatie
                  &lt;/td&gt;
                  &lt;td&gt;
                      &lt;telerik:RadComboBox ID="rcbLocation" runat="server" Width="250px" ValidationGroup="NewResource"
                          DataTextField="location" DataValueField="Location_ID" AppendDataBoundItems="true" /&gt;
                  &lt;/td&gt;
              &lt;/tr&gt;
          &lt;/telerik:RadAjaxPanel&gt;
      &lt;/table&gt;
  &lt;/FormTemplate&gt;
  </code></pre>
  
  <p>How can you make this work? If it's impossible, please give alternative approaches that don't require much work.</p>