down load files

 string FilePath = Server.MapPath(Request.ApplicationPath) + "\\attachment\\" + "20070924661.JPG";
        FileInfo fi = new FileInfo(FilePath);
        FileStream fs = new FileStream(FilePath, FileMode.Open);
        byte[] bytes = new byte[(int)fs.Length];
        fs.Read(bytes, 0, bytes.Length);
        fs.Close();
        Response.Clear();
        Response.ContentType = "application/octet-stream";
        Response.AddHeader("Content-Disposition", "attachment; filename=" + HttpUtility.UrlEncode(fi.Name, System.Text.Encoding.UTF8).Replace("+", " "));

        Response.BinaryWrite(bytes);
        Response.End();

    //    string att = Server.MapPath(Request.ApplicationPath) + "\\attachment\\" + (string)but.Text;
    //    Response.Charset = "utf-8";
    //    Response.Buffer = true;
    //    this.EnableViewState = false;
    //    Response.ContentEncoding = System.Text.Encoding.Default;
    //    Response.AddHeader("Content-Disposition", "attachment; filename=" + but.Text); //' 注意name1　和name de qu别
    //    Response.ContentType = "application/" + Path.GetExtension(but.Text);
    //    Response.WriteFile(att);
    //    Response.End()