由于我将我的网站从 .NET 4.0 更改为 3.5 ModalPopup 无法正常工作。问题是没有显示错误消息。所以我不知道如何解决它。以前有人遇到过同样的问题吗?
<%@ Page Language="C#" AutoEventWireup="true" CodeFile="Default.aspx.cs" Inherits="_Default" %>
<%@ Register Assembly="AjaxControlToolkit" Namespace="AjaxControlToolkit" TagPrefix="asp" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title></title>
</head>
<body>
    <form id="form1" runat="server">
    <asp:ScriptManager ID="ScriptManager1" runat="server">
    </asp:ScriptManager>
    <div>
        <asp:Button ID="btnpopup" runat="server" Text="Button" /> 
        <asp:ModalPopupExtender ID="mpe" runat="server" TargetControlID="btnpopup" PopupControlID="pnlpopup" 
            CancelControlID="btnCancelpopup" EnableViewState="true" DropShadow="true" />
            <asp:Panel ID="pnlpopup" runat="server" Width="400px">
                test
            <asp:Button ID="btnCancelpopup" runat="server" Text="Button" />
        </asp:Panel>
    </div>
    </form>
</body>
</html>