Closed Issue: CustomValidator and ValidatorCalloutExtender cause script error on post back [20094]

<%@ Register Assembly="Validators" Namespace="Sample.Web.UI.Compatibility" TagPrefix="cc1" %>
........................
<asp:UpdatePanel ID="MainUpdatePanel" runat="server">
<ContentTemplate>
<cc1:CustomValidator ID="cvCountry" runat="server" ClientValidationFunction="cvCheckCountry_Validate" EnableClientScript=true
Display="None" ErrorMessage="Please select country!" SetFocusOnError=true ValidationGroup="REG"/>
<ajax:ValidatorCalloutExtender ID="ValidatorCalloutExtender1" runat="server" TargetControlID="cvCountry"
Width="300px" />
...............
</ContentTemplate>
</asp:UpdatePanel>

When I try to submit the form I get the following JavaScript error:

Microsoft JScript runtime error: Sys.ArgumentUndefinedException: Value cannot be undefined.
Parameter name: id


I saw that this error had been fixed already but in my case it repeats 100%. AJAX DLL version 3 . 0 . 2 0 8 2 0 . 1 6 5 9 8

How to fix this error? I tried to use validators from http://blogs.msdn.com/mattgi/archive/2007/01/23/asp-net-ajax-validators.aspx but no luck.
Comments: Please upgrade to the latest version of AJAX Control Toolkit v15.1. If the problem remains, feel free to post a new issue.