Look at your tagPrefix - cc1
Where are your TargetID's pointing to?
Have you added the ScriptManager?
I'm not sure should AjaxToolKit be replaced with cc1?
<cc1:ModalPopupExtender ID="ModalPopupExtenderLogin" runat="server"
TargetControlID="Loginlnk"
PopupControlID="LoginPanel"
BackgroundCssClass="modalBackground"
DropShadow="true"
OkControlID="LoginBtn"
OnOkScript="ok()"
CancelControlID="CancelBtn"
X="650" Y="140"
/>