<cc2:ModalPopupExtender ID="ModalPopupExtender1" runat="server" BackgroundCssClass="modalBackground" PopupControlID="panel1" DropShadow="true" CancelControlID="CancelButton" TargetControlID="Button1">
</cc2:ModalPopupExtender>
在IE6里,背景层没有挡住Dropdownlist,可是在IE7里,Dropdownlist看都看不到了.