文件下载无法下载，只能用迅雷下载，怎么回事

Question

在ASP.NET4.0，IE8,winXP下，如下代码： protected void DownloadFile(string fileName, string saveFileName)
        {
            System.IO.FileInfo fileInfo = new System.IO.FileInfo(fileName);
            Response.Clear();
            Response.AddHeader(DString.CONTENT_DIS, string.Format(DString.EXCLE_NAME, saveFileName));
            Response.AddHeader(DString.FILE_LENGTH, fileInfo.Length.ToString());
            Response.ContentType = DString.EXCLE_MINI;
           
            Response.WriteFile(fileInfo.FullName);            Response.End();
        } protected void btn_Download_Click(object sender, EventArgs e)
        {
            string fileName;
            string saveFile;
            fileName = MapPath(DString.EVALUATION_FILE_PATH);
            CreateScoreEvaluation(fileName);
            saveFile = "质量分析表";
            DownloadFile(fileName, saveFile);
        }发现无法正常下载，该项目中有好几处下载都是使用同一段下载代码，但有的能正常下载，有的却不能，报错：“无法打开xxx.aspx站点”，试着安装迅雷，发现，会自动打开迅雷下载，而且能成功下载，实在搞不起清楚是咋回事，我不能要求客户都安装迅雷，所以请高手帮助，谢谢！貌似在win7+IE9下没有此问题

Answer 1

            string DownAdress=fileName
            if (!File.Exists(Server.MapPath(DownAdress)))
            {
                Response.Write("下载的文件不存在!");
                Response.End();
                return;
            }
            using (FileStream fso = new FileStream(Server.MapPath(DownAdress), FileMode.Open,FileAccess.ReadWrite,FileShare.Inheritable))
            {
                string[] filename=DownAdress.Split(new char[]{'/'});
                int len = Convert.ToInt32(fso.Length);
                byte[] FileObj = new byte[len];
                fso.Read(FileObj, 0, len);
                Response.AddHeader("Content-Disposition", string.Format("attachment; filename={0}", HttpUtility.UrlEncode(filename[filename.Length - 1]), System.Text.Encoding.UTF8));
                Response.AddHeader("Content-Length", len.ToString());
                Response.ContentType = "application/octet-stream";
                Response.Charset = "UTF-8";
                Response.ContentEncoding = System.Text.Encoding.UTF8; 
                Response.BinaryWrite(FileObj);
                Response.Flush();
                Response.Clear();
                fso.Close();
            }

Answer 2

            Response.AddHeader(DString.CONTENT_DIS, string.Format(DString.EXCLE_NAME, saveFileName));
            Response.ContentType = DString.EXCLE_MINI;这分别是什么值？
另外在   Response.End(); 前 你可以写 Response.Flush();