/// <summary>
        /// 上传单个文件
        /// </summary>
        /// <param name="File1">文件控件</param>
        /// <param name="sizes">上传大小限制,KB单位；为小于等于0不限</param>
        /// <param name="filetype">文件后缀限定，以“|”隔开，不带"."号。为空不限</param>
        /// <param name="filepath">上传到文件夹路径，为空为当前文件夹</param>
        /// <param name="returnmessage">上传返回信息</param>
        /// <returns>返回上传的文件名虚拟路径</returns>
        public static string UploadFile(System.Web.UI.HtmlControls.HtmlInputFile File1, int sizes, string filetype, string filepath,ref string returnmessage)
        {
            returnmessage = "";
            try
            {
                filepath = filepath.Trim();
                if (filepath.LastIndexOf("/") != filepath.Length - 1)
                {
                    filepath += "/";
                }
                string path = filepath; //保存至的文件夹
                if (path == "")
                {
                    path = "./";
                }
                path = System.Web.HttpContext.Current.Server.MapPath(path);

                //判断是否有上传的文件
                string sourcepath = File1.Value.Trim();//文件的上传的路径
                if (sourcepath == "" || sourcepath == null)
                {
                    returnmessage = "无上传文件";
                    return "";
                }

                string tfiletype = sourcepath.Substring(sourcepath.LastIndexOf(".") + 1).ToLower();
                //如果要求的后缀不为空则判断上传的文件的后缀是否合适
                if (filetype != "")
                {
                    if ((filetype.ToLower() + "|").IndexOf(tfiletype + "|") < 0)
                    {
                        returnmessage = "上传的文件类型不符合设定";
                        return "";
                    }
                }

                if (sizes > 0)
                {
                    int sizes2 = sizes * 1024;
                    //获得上传文件的大小
                    long strLen = File1.PostedFile.ContentLength;
                    //判断上传文件大小
                    if (strLen > sizes2)
                    {
                        returnmessage = "上传的文件不能大于" + sizes.ToString() + "KB";
                        return "";
                    }
                }

                System.IO.DirectoryInfo dir = new System.IO.DirectoryInfo(path);
                //判断文件夹否存在,不存在则创建
                if (!dir.Exists)
                {
                    dir.Create();
                }

                string modifyfilename = Tools.GetId(0,12);
                path = path + modifyfilename + "." + tfiletype;
                while (System.IO.File.Exists(path))
                {
                    modifyfilename = Tools.GetId(0, 12);
                    path = path + modifyfilename + "." + tfiletype;
                }
                File1.PostedFile.SaveAs(path);
                filepath = filepath + modifyfilename + "." + tfiletype;
                returnmessage = "上传成功";
                return filepath;
            }
            catch
            {
                returnmessage = "上传出现错误";
                return "";
            }
        }

------解决方案--------------------
 string fileType = this.upSheetFile.PostedFile.ContentType;
       if (fileType != "text/xml")
       {
           this.lblErr.Text = "上传文件类型不正确！";
           return;
       }

       if (this.upSh