我的代码是
请给我解决方案...谢谢
  bool b = false;
  string str=Server.MapPath("~/Files/"+filepath);
      //  Send the file to the browser
      Response.AddHeader("Content-type", filetype);
      Response.AddHeader("Content-Disposition", "attachment; filename=" + filename);
      Response.TransmitFile(Server.MapPath("~/Files/" + filepath));
      Response.Flush();
      //  HttpContext.Current.ApplicationInstance.CompleteRequest();
       Response.End();
      b = true;