Error attaching entity of id when trying to update MVC5

Question

Hi,

 

I am getting error whed trying to update table.

 

public static int Partner_AddUpdate(Partner t_Entity)
        {
            int retValue = -1;
            using (var t_Context = new ReboxEntities())
            {
                using (var transaction = t_Context.Database.BeginTransaction())
                {
                    try
                    {
                        if (t_Entity.idPartner > 0)
                        {
                            Partner t_EntityModified = t_Context.Partners.Single(m => m.idPartner == t_Entity.idPartner);

                            t_Entity.LoginName = t_EntityModified.LoginName;
                            t_Entity.Password = t_EntityModified.Password;
                            t_Entity.PartnerTypeName = t_EntityModified.PartnerTypeName;
                            t_Entity.IncorporationType = t_EntityModified.IncorporationType;

                            t_Context.Entry(t_Entity).State = System.Data.Entity.EntityState.Modified;
                        }
                        else
                        {
                            t_Context.Entry(t_Entity).State = System.Data.Entity.EntityState.Added;
                        }

                        t_Context.SaveChanges();

                        retValue = t_Entity.idPartner;

                        transaction.Commit();
                    }
                    catch (Exception exc)
                    {
                        transaction.Rollback();
                    }
                }
            }
            return retValue;
        }