RadAjaxManagerProxy Issue

[jerry]

Whenever I add this piece of code

<telerik:RadAjaxManagerProxy ID="RadAjaxManagerProxy1" runat="server">
        <AjaxSettings>
          <telerik:AjaxSetting AjaxControlID="ddlStudy">
            <UpdatedControls>
              <telerik:AjaxUpdatedControl ControlID="lstDataset" />
            </UpdatedControls>
          </telerik:AjaxSetting>
        </AjaxSettings>
      </telerik:RadAjaxManagerProxy>

I get this poping up next to my List Box(lstDataset) - I don't have a lstDatasetPanel within my project.
2715|updatePanel|ctl00_ctl00_ContentPlaceHolder1_lstDatasetPanel

What i'm doing is on change of a drop down I want to populate the list box with the data.  When I try and change the drop down more then once it gives me this error:

"Microsoft JScript runtime error: Sys.InvalidOperationException: Could not find UpdatePanel with ID 'ctl00_ctl00_ContentPlaceHolder1_lstDatasetPanel'. If it is being updated dynamically then it must be inside another UpdatePanel."

Thank You
Jerry