Data entity modelconfiguration modelvalidationexception when insert database

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C#

forms

entity-framework

i'm beginer to Entity Framework
Data Entity ModelConfiguration ModelValidationException when insert data odatabase
what is the wrong in my code?
Thank in advance!

This is my Object Class

[Table ("customerDetails")]
    class customerDetails
    {
        [Key]
        internal int cusId { get; set; }
        internal string cusName { get; set; }
        internal string cusNic { get; set; }
        internal string cusAdd { get; set; }
        internal DateTime cusDob { get; set; }
    }.

This is DbContext

class cusSave : DbContext
    {
        public cusSave() : base(@"Server= servername"
                            + "; Database= dbname"
                            + "; UID= user"
                            + "; Pwd= pass") { }
        public DbSet<customerDetails> saveCus { get; set; }
    }

This is the btn Event

private void btnSave_Click(object sender, EventArgs e)
        {
            var cus =new Logic.customerDetails
            {
                cusId = Convert.ToInt32(txtCusId.Text),
                cusName = txtcusName.Text,
                cusAdd = txtcusAdd.Text,
                cusNic = txtcusNic.Text,
                cusDob = dtpDob.Value
            };
                var saveCus = new Logic.cusSave();
                saveCus.saveCus.Add(cus);
                saveCus.SaveChanges();
        }

Solution here
Change object class like this
Thanks Every One
Specially Graeme_Grant

class customerDetails
    {
        [Key]
        public int cusId { get; set; }
        public string cusName { get; set; }
        public string cusNic { get; set; }
        public string cusAdd { get; set; }
        public DateTime cusDob { get; set; }
    }

What I have tried:

check all object values before save when assign to object but nothings wrong