AsyncFileUpload上传失败提示The file attached is invalid是什么原因

Question

AsyncFileUpload上传失败提示The file attached is invalid是什么原因？
主要代码如下：
<asp:AsyncFileUpload ID="afuPicAgency" runat="server" 
                    onclientuploadcomplete="afuPicAgency_UploadComplete" ThrobberID="Uploading" 
                    UploadingBackColor="#666699" 
                    onclientuploaderror="afuPicAgency_UploadError" 
                    onclientuploadstarted="afuPicAgency_UploadStarted" 
                    onuploadedcomplete="afuPicAgency_UploadedComplete" 
                    onuploadedfileerror="afuPicAgency_UploadedFileError" UploaderStyle="Modern" />
                <asp:Image ID="Uploading" runat="server" ImageUrl="/Images/loading.gif" Height="21px" Width="21px" />
                <asp:Label ID="lblUploadStatus" runat="server" Text="请选择文件" ClientIDMode="Static"></asp:Label>function afuPicAgency_UploadError(sender, args) {
            document.getElementById('lblUploadStatus').innerText = "对不起，文件“" + args.get_fileName() + "”上传出错，原因：" + args.get_errorMessage();
        }
        function afuPicAgency_UploadStarted(sender, args) {
            document.getElementById('lblUploadStatus').innerText = "文件“" + args.get_fileName() + "”正在上传，请稍等";
        }
        function afuPicAgency_UploadComplete(sender, args) {
            document.getElementById('lblUploadStatus').innerText = "文件“" + args.get_fileName() + "”上传完成，文件大小：" + args.get_length() + " bytes";
        }在后台UploadedFileError中断查看了一下，filename和filesize都是为空的，但不知道为什么会这样，上传的也就是普通的图片文件

Answer 1

  <asp:Image ID="Uploading" runat="server" ImageUrl="/Images/loading.gif" Height="21px" Width="21px" />
                <asp:Label ID="lblUploadStatus" runat="server" Text="请选择文件" ClientIDMode="Static"></asp:Label>
看看你的id是不是变了，服务器控件经常变id