what is this update panel error?
<p>I am using the model poop up in my below code i am getting the following error what may be the reason?</p>

<pre><code>Cannot unregister UpdatePanel with ID 'updatePnl' since it was not registered with the ScriptManager. This might occur if the UpdatePanel was removed from the control tree and later added again, which is not supported.
Parameter name: updatePanel



&lt;telerik:GridTemplateColumn HeaderStyle-Width="20%" HeaderText="See Your Assessment"&gt;
                    &lt;ItemTemplate&gt;
                        &lt;asp:Button CommandName="Show" OnClick="grdMasterbtnClick" CommandArgument='&lt;%#Eval("SurveyClientID")%&gt;'
                            ID="btn" runat="server" Text="Your Assessment" /&gt;
                        &lt;cc1:ModalPopupExtender CancelControlID="btnCancel" PopupControlID="modelPopUp" ID="ModalPopupExtender1"
                            runat="server" TargetControlID="imgClientFreeEval"&gt;
                        &lt;/cc1:ModalPopupExtender&gt;
                        &lt;asp:UpdatePanel ID="updatePnl" runat="server"&gt;
                            &lt;ContentTemplate&gt;
                                &lt;asp:Panel ID="modelPopUp" runat="server" Visible="false" BackColor="AliceBlue"&gt;
                                    &lt;p&gt;
                                        These items will be permanently deleted and cannot be recovered. Are you sure?
                                    &lt;/p&gt;
                                    &lt;asp:Button ID="btnOk" Text="OK" runat="server" /&gt;
                                    &lt;asp:Button ID="btnCancel" Text="Cancel" runat="server" /&gt;
                                &lt;/asp:Panel&gt;
                            &lt;/ContentTemplate&gt;
                        &lt;/asp:UpdatePanel&gt;
                    &lt;/ItemTemplate&gt;
                    &lt;HeaderStyle Width="20%"&gt;&lt;/HeaderStyle&gt;
                &lt;/telerik:GridTemplateColumn&gt;
</code></pre>
