ajaxToolkit控件事件一直不能执行

AjaxFileUpload在使用时，一直处于uploading的状态，是为什么？

 <asp:ScriptManager ID="ScriptManager1" runat="server"></asp:ScriptManager>
            <ajaxToolkit:AjaxFileUpload ID="AjaxFileUpload1" runat="server" OnUploadComplete="AjaxFileUpload1_UploadComplete" OnUploadCompleteAll="AjaxFileUpload1_UploadCompleteAll" OnUploadStart="AjaxFileUpload1_UploadStart" Mode="Auto" />

  protected void AjaxFileUpload1_UploadComplete(object sender, AjaxControlToolkit.AjaxFileUploadEventArgs e) {
            Response.Write("<script>alert('AjaxFileUpload1_UploadComplete!')</script>");
            string path = string.Format(@"~/Images/{0}", e.FileName);
            AjaxFileUpload1.SaveAs(Server.MapPath(path));
        }

        protected void AjaxFileUpload1_UploadCompleteAll(object sender, AjaxControlToolkit.AjaxFileUploadCompleteAllEventArgs e) {
            Response.Write("<script>alert('AjaxFileUpload1_UploadCompleteAll!')</script>");
        }

        protected void AjaxFileUpload1_UploadStart(object sender, AjaxControlToolkit.AjaxFileUploadStartEventArgs e) {
            Response.Write("<script>alert('AjaxFileUpload1_UploadStart!')</script>");
        }

http://bbs.csdn.net/topics/360097530