public partial class Categoies
 {
  public Categoies()
  {
  this.Posts = new HashSet<Posts>();
  }
 
  public int Id { get; set; }
  public string Name { get; set; }
  public string Description { get; set; }
  public Nullable<int> PositionId { get; set; }
 
  public virtual CategoryPositions CategoryPositions { get; set; }
  public virtual ICollection<Posts> Posts { get; set; }
 }

public class CategoriesViewModel
 {
  public int Id { get; set; }
 
  [Required(ErrorMessage = "{0} alanı boş bırakılmamalıdır!")]
  [Display(Name = "Kategori Adı")]
  public string Name { get; set; }
 
  [Display(Name = "Kategori Açıklama")]
  public string Description { get; set; }
 
  [Display(Name = "Kategori Pozisyon")]
  [Required(ErrorMessage="{0} alanı boş bırakılmamalıdır!")]
  public int PositionId { get; set; }
 }

Mapper.CreateMap<CategoriesViewModel, Categoies>()
  .ForMember(c => c.CategoryPositions, option => option.Ignore())
  .ForMember(c => c.Posts, option => option.Ignore());

[HttpPost]
 public ActionResult _EditCategory(CategoriesViewModel viewModel)
 {
  using (NewsCMSEntities entity = new NewsCMSEntities())
  {
  if (ModelState.IsValid)
  {
  try
  {
  category = entity.Categoies.Find(viewModel.Id);
  AutoMapper.Mapper.Map<CategoriesViewModel, Categoies>(viewModel, category);
  //category = AutoMapper.Mapper.Map<CategoriesViewModel, Categoies>(viewModel);
  //AutoMapper.Mapper.Map(viewModel, category);
  entity.SaveChanges();
 
  // Veritabanı işlemleri başarılı ise yönlendirilecek sayfayı 
  // belirleyip ajax-post-success fonksiyonuna gönder.
  return Json(new { url = Url.Action("Index") });
  }
  catch (Exception ex)
  {
 
  }
  }
 
  // Veritabanı işlemleri başarısız ise modeli tekrar gönder.
  ViewBag.Positions = new SelectList(entity.CategoryPositions.ToList(), "Id", "Name");
  return PartialView(viewModel);
  }
 }

protected void Application_Start()
 {
  InitializeAutoMapper.Initialize();
 }

public static class InitializeAutoMapper
 {
  public static void Initialize()
  {
  CreateModelsToViewModels();
  CreateViewModelsToModels();
  }
 
  private static void CreateModelsToViewModels()
  {
  Mapper.CreateMap<Categoies, CategoriesViewModel>();
  }
 
  private static void CreateViewModelsToModels()
  {
  Mapper.CreateMap<CategoriesViewModel, Categoies>()
  .ForMember(c => c.CategoryPositions, option => option.Ignore())
  .ForMember(c => c.Posts, option => option.Ignore());
  }
 }

Missing type map configuration or unsupported mapping. Mapping types: CategoriesViewModel -> Categoies_7314E98C41152985A4218174DDDF658046BC82AB0ED9E1F0440514D79052F84D NewsCMS.Areas.Admin.Models.CategoriesViewModel -> System.Data.Entity.DynamicProxies.Categoies_7314E98C41152985A4218174DDDF658046BC82AB0ED9E1F0440514D79052F84D

Destination path: Categoies_7314E98C41152985A4218174DDDF658046BC82AB0ED9E1F0440514D79052F84D

Source value: NewsCMS.Areas.Admin.Models.CategoriesViewModel