Microsoft JScript runtime error: 'getAt(...).id' is null or not an object

[simonmicheal]

<ext:ToolbarButton ID="btnSaveRecord1" runat="server" Icon="Disk" Text="Save">
                    <AjaxEvents>
                        <Click OnEvent="Save_Click" Before="return #{FormPanel1}.getForm().isValid();" Success="Ext.Msg.alert('', 'Saved');">
                            <ExtraParams>
                                <ext:Parameter Name="recordId" Value="#{StoreComments}.getAt(0).id" Mode="Raw" />
                            </ExtraParams>
                        </Click>
                    </AjaxEvents>
                </ext:ToolbarButton>

Keep getting this error, my original form is a popup window.

Thanks