Remove Calendarextender from DIV and do as following
<cc1:CalendarExtender ID="ceadt" runat="server" TargetControlID="txtaaadate" OnClientShown="OnClientShown">
</cc1:CalendarExtender>
<script type="text/javascript">
function OnClientShown(sender, args) {
sender._popupBehavior._element.style.zIndex = 10005;
}
</script>