Ora mi da il seguente errore in db.SaveChanges()

codice:
Validation failed for one or more entities. See 'EntityValidationErrors' property for more details.
codice:
        [HttpPost]
        public ActionResult EditPrimicinque(List<User> users)
        {
            if (ModelState.IsValid)
            {
                foreach(User user in users)
                    db.Entry(user).State = EntityState.Modified;

                db.SaveChanges();
                return RedirectToAction("Index");
            }
            return View(user);
        }

Qualche idea???