I have a small asp.net MVC 1 web app that can store files and create directories in the App_Data directory. When the write operation succeeds, I add a message to the tempdata and do a redirectToRoute. The problem is that the tempdata is null when the action is executed. If i write the files in a directory outside of the web applications root directory, the tempdata is not null and everything works correctly. Any ideas why writing in the app_data seems to clear the tempdata ? edit: if DRS.Logic.Repository.Manager.CreateFile(path, hpf, comment) writes in the App_Data, TempData will be null in the action being redirected to. if it is a directory out of the web app root it is fine. No exceptions are being thrown. [AcceptVerbs(HttpVerbs.Post)] public ActionResult Create(int id, string path, FormCollection form) { ViewData["path"] = path; ViewData["id"] = id; HttpPostedFileBase hpf; string comment = form["FileComment"]; hpf = Request.Files["File"] as HttpPostedFileBase; if (hpf.ContentLength != 0) { DRS.Logic.Repository.Manager.CreateFile(path, hpf, comment); TempData["notification"] = "file was created"; return RedirectToRoute(new { controller = "File", action ="ViewDetails", id = id, path = path + Path.GetFileName(hpf.FileName) }); } else { TempData["notification"] = "No file were selected."; return View(); } }