Validation failed for one or more entities. See entityvalidationerrors property for more details.

try
{
    // Your code...
    // Could also be before try if you know the exception occurs in SaveChanges

    context.SaveChanges();
}
catch (DbEntityValidationException e)
{
    foreach (var eve in e.EntityValidationErrors)
    {
        Console.WriteLine("Entity of type \"{0}\" in state \"{1}\" has the following validation errors:",
            eve.Entry.Entity.GetType().Name, eve.Entry.State);
        foreach (var ve in eve.ValidationErrors)
        {
            Console.WriteLine("- Property: \"{0}\", Error: \"{1}\"",
                ve.PropertyName, ve.ErrorMessage);
        }
    }
    throw;
}

---AND---

Quote:

Error: Validation failed for one or more entities. See 'EntityValidationErrors' property for more details.

public partial class ContactDetail
    {
        [StringLength(10)]
        public string OfficeEmail { get; set; }
    }

solution: correct your Data Model according to your database SET fieldNames or length.

public partial class ContactDetail
    {
        [StringLength(50)]
        public string OfficeEmail { get; set; }
    }

All good suggestions above. In fact, I solved my issue using Yogeesha's catch block above. It may be important to file this error away in your head, because you may run into this again. For me, I was passing a null value into a table field that had a NOT NULL declaration. So, really, I would have solved this if I had just looked at the table fields.