Using Button Inside Ajax Pop Up Extender Give Me that error on Click : Microsoft JScript runtime error: 'this._postBackSettings.async' is null or not an object

I'm Using Ajax POP UP Extender Control ... and The Panel Which will appear in The POP UP Has Data List ... Inside That DataList i have Image Button For Each Item In Data List.... When I click in any Image Button in That DataList ......I Get That Error At run time Microsoft JScript runtime error: 'this._postBackSettings.async' is null or not an object

... My ASPX Code is

<asp:HyperLink ID="lnkMainRoomDetails" runat="server" style="cursor:pointer; margin-left: .2cm">View Room Details</asp:HyperLink><asp:Panel ID="MainPanel2" runat="server" BackColor="Black"><asp:DataList ID="dlMainPicturesButtons" runat="server" DataKeyField="ID" RepeatDirection="Horizontal"><ItemTemplate><asp:ImageButton UseSubmitBehavior="false" BorderColor="Silver" BorderWidth="1px" ID="btnMainPictureButton"
                                                                                        runat="server" Height="30px" ImageUrl='<%# Eval("PathURL", "../{0}") %>' Width="60px"
                                                                                        OnClick="btnMainPictureButton_Click" /></ItemTemplate></asp:DataList></asp:Panel><asp:PopupControlExtender ID="Panel2_PopupControlExtender" runat="server" PopupControlID="MainPanel2"
                                                        TargetControlID="lnkMainRoomDetails" CacheDynamicResults="True"></asp:PopupControlExtender>

And I put that code inside update panel and ToolkitScriptManager