Entity Framework OptimisticConcurrencyException: Store update, insert, or delete statement affected an unexpected number of rows

 If i am using adding , then it's add new row, but i want to update row data.when using modified then on DB.SaveChanges() it showing exception.Means i am not able to update.

OptimisticConcurrencyException: Store update, insert, or delete statement affected an unexpected number of rows (0). Entities may have been modified or deleted since entities were loaded.

        [HttpPost]
        public ActionResult EditCategory(int id,tbl_Category category, HttpPostedFileBase file)
        {
            tbl_Category ctgry = new tbl_Category();
            if (file != null && file.ContentLength > 0)
                try
                {
                    string folderpath = Server.MapPath("~/Images/category_Images");
                    string filename = Path.GetFileName(file.FileName);
                    string extension = Path.GetExtension(file.FileName);
                    string path = Path.Combine(Server.MapPath("~/Images/category_Images"),
                                               Path.GetFileName(file.FileName));
                    file.SaveAs(path);
                    ctgry.Image = filename;
                }
                catch { }
                    ctgry.CategoryName = category.CategoryName;
            ctgry.Status = category.Status;
            DB.Entry(ctgry).State = EntityState.Modified;
            //DB.Entry(ctgry).State = EntityState.Added;
            DB.SaveChanges();
            return RedirectToAction("Category");
        }