Regular expression exception

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ASP.NET

.NET

entity-framework

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Model class:

[RegularExpression(@"^(?=*[A-Z])(?=*[a-z])(?=*[0-9])[A-Za-z0-9]{8,}$", ErrorMessage = "invalid")]
       [Required(ErrorMessage = "Required")]
       [StringLength(65)]
       [Display(Name = "Password")]
      // [RegularExpression(@"^(?=.*[a-z])(?=.*[A-Z])(?=.*\d)[a-zA-Z\d]{8,}$", ErrorMessage = "Password contains invalid characters")]
       //[DataType(DataType.Password)]
       public string password { get; set; }

Login Action method:

public ActionResult Login(Login loginForm, string returnUrl)
       {
           if (!ModelState.IsValid) return View("Login");
           var Password = Md5Hash.Encrypt(loginForm.Password);

           var user = (from users in _dbContextModel.user_login
                       where ((users.login_id == loginForm.Login_id) && (users.password == Password))
                       select users).FirstOrDefault();

           if (user != null)
           {
               UserLogin userLogin = user;
               userLogin.last_login = DateTime.Now;

              // userLogin.password = user.password;

               _dbContextModel.Entry(userLogin).State = EntityState.Modified;
               _dbContextModel.SaveChanges();

When i am using above regular expression, i am facing the following run-time exception why? please give me solution. I am using linq, E.F7 and MVC5 using VS015 and .net framework 4.5

My ERROR IS:
Validation failed one or more entity

What I have tried:

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