Maskededit Extender for date is not working in Model Frmae

Iam using MaskedEditExtender for date textbox in a popup .aspx popup window page. When popup window is loading it is showing a javascript runtime error "Microsoft JScript runtime error: Unspecified error." Below is my code:
<label style="width:40px">Date:</label> <asp:TextBox ID="txtDate" CssClass="calendarField" runat="server"></asp:TextBox> <cc1:CalendarExtender ID="DateCalExtender" runat="server" TargetControlID="txtDate" PopupButtonID="imgDate" PopupPosition="Right" CssClass="Calendar"/> <asp:LinkButton runat="server" CssClass="calendarButton" ID="imgDate" Text="<img border='0' class='calendarButton' src='Images/coreCalendarIcon.gif'>"></asp:LinkButton> <cc1:MaskedEditExtender ID="MaskedEditExtender3" runat="server" TargetC ...