I created a page with a button inside an update panel with an UpdatePanelAnimationExtender. When the button property UseSubmitBehavior is set to false, the page throws the following error the first time the button is clicked. This problem started after upgrading to AjaxControlToolkit v15.1.4 and .NET 4.5.1
Uncaught TypeError: Cannot read property 'id' of undefined
Sys.Extended.UI.Animation.UpdatePanelAnimationBehavior._partialUpdateBeginRequest @ ScriptResource.axd?d=…:74
(anonymous function) @ ScriptResource.axd?d=…:47
(anonymous function) @ ScriptResource.axd?d=…:3484
Sys$WebForms$PageRequestManager$_onFormSubmit @ ScriptResource.axd?d=…:1284
Sys$WebForms$PageRequestManager$_doPostBack @ ScriptResource.axd?d=…:824
(anonymous function) @ ScriptResource.axd?d=…:47
onclick @ default.aspx:67
<%@ Page Language="VB" AutoEventWireup="false" CodeFile="Default.aspx.vb" Inherits="_Default" %><!DOCTYPE html><html xmlns="http://www.w3.org/1999/xhtml"><head runat="server"><title></title></head><body><form id="form1" runat="server"><div><asp:ScriptManager ID="ScriptManager1" runat="server"></asp:ScriptManager><asp:UpdatePanel ID="UpdatePanel1" runat="server"><ContentTemplate><asp:Button ID="Button1" runat="server" Text="Button" UseSubmitBehavior="false" /></ContentTemplate></asp:UpdatePanel><ajaxToolkit:UpdatePanelAnimationExtender ID="upae" BehaviorID="animation" runat="server" TargetControlID="UpdatePanel1"><Animations><OnUpdating><Parallel duration="0"><ScriptAction Script="onUpdating();" /> </Parallel></OnUpdating><OnUpdated><Parallel duration="0"><ScriptAction Script="onUpdated();" /> </Parallel> </OnUpdated></Animations></ajaxToolkit:UpdatePanelAnimationExtender><script type="text/javascript" language="javascript">
function onUpdating() {
//start doing something
}
function onUpdated() {
//stop doing something
}</script></div></form></body></html>