AjaxToolKit Issues in Modal Popup in IE 10

I have a following implementation in an asp.net application.

In abc.aspx i have this tag:

<ajaxToolkit ModalPopUpExtender popupControId="pnl"><asp:Panel id="pnl"><iframe src="example.aspx" id="fr2"></asp:Panel>

Now the example.aspx has a PopUp Control Extender as like this

<asp:Textbox id="txt"><asp:UpdatePanel id=udp><ContentTemplate><asp:Button/><asp:CheckBoxList><asp:Button/> .</ContentTemplate></asp:UpdatePanel><ajaxToolkit:PopUpControlExtender targetControlId="txt"></ajaxToolkit>

Now that PopupControlExtender in example.aspx runs fine when it is normally rendered as an aspx page.When the Page is Implemented as above in an iframe,in IE10, the PopUp Control Extender Doesnot Work as Desired.But it Works Fine In compatibility modes of IE as Well as Normal modes in Firefox,Chrome and Safari.

Please Help on this ..