error in asp.net mvc3

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

public ActionResult Edit(int id)
        {
            Album album = db.Albums.Find(id);
            ViewBag.GenreId = new SelectList(db.Genres, "GenreId", "Name", album.GenreId);
            ViewBag.ArtistId = new SelectList(db.Artists, "ArtistId", "Name", album.ArtistId);
            return View(album);
        }

[HttpPost]
       public ActionResult Edit(Album album)
       {
           if (ModelState.IsValid)
           {
               db.Entry(album).State = EntityState.Modified;
               db.SaveChanges();
               return RedirectToAction("Index");
           }
           ViewBag.GenreId = new SelectList(db.Genres, "GenreId", "Name", album.GenreId);
           ViewBag.ArtistId = new SelectList(db.Artists, "ArtistId", "Name", album.ArtistId);
           return View(album);
       }

namespace MusicStore.Models
{
    [Bind(Exclude="AlbumId")]
    public class Album
    {
        [ScaffoldColumn(false)]
        public int AlbumId { get; set; }

        [DisplayName("Genre")]
        public int GenreId { get; set; }

        [DisplayName("Artist")]
        public int ArtistId { get; set; }

        [Required(ErrorMessage="An Album title is required")]
        [StringLength(160)]
        public string Title { get; set; }

        [Required(ErrorMessage = "Price is required")]
        [Range(0.01,100.00,ErrorMessage="Price must be between 0.01 and 100.00")]
        public decimal Price { get; set; }
        public string AlbumArtUrl { get; set; }
        public Artist Artist { get; set; }

        public Genre Genre { get; set; }
    }
}