Column Discriminator error EF code first

I'm doing a project in asp.net, I'm using C # classes to make the connection to the database, but every time I try to insert a user into the database, it generates the following error:

  

invalid column name "Discriminator"

Note: My bank already existed, I used the code first from database.

This is my method of registering:

public virtual void cadastrar(T item) 
{
    context.Set<T>().Add(item);
    context.SaveChanges();

}

The class EF generated:

using System;
using System.Data.Entity;
using System.ComponentModel.DataAnnotations.Schema;
using System.Linq;

public partial class Banco : DbContext
{
    public Banco()
        : base("BDbuffet")
    {
    }

    public virtual DbSet<Alimento> Alimentos { get; set; }
    public virtual DbSet<Bebida> Bebidas { get; set; }
    public virtual DbSet<Festa> Festas { get; set; }
    public virtual DbSet<Garcon> Garcons { get; set; }
    public virtual DbSet<GarconsContratado> GarconsContratados { get; set; }
    public virtual DbSet<Iten> Itens { get; set; }
    public virtual DbSet<sysdiagram> sysdiagrams { get; set; }
    public virtual DbSet<Usuario> Usuarios { get; set; }

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        modelBuilder.Entity<Alimento>()
            .Property(e => e.nome)
            .IsUnicode(false);

        modelBuilder.Entity<Alimento>()
            .Property(e => e.descricao)
            .IsUnicode(false);

        modelBuilder.Entity<Alimento>()
            .Property(e => e.imagemAlimento)
            .IsUnicode(false);

        modelBuilder.Entity<Alimento>()
            .Property(e => e.valorUnitario)
            .HasPrecision(19, 4);

        modelBuilder.Entity<Alimento>()
            .HasMany(e => e.Itens)
            .WithOptional(e => e.Alimento)
            .HasForeignKey(e => e.idAlimentos);

        modelBuilder.Entity<Bebida>()
            .Property(e => e.nome)
            .IsUnicode(false);

        modelBuilder.Entity<Bebida>()
            .Property(e => e.descricao)
            .IsUnicode(false);

        modelBuilder.Entity<Bebida>()
            .Property(e => e.imagemBebida)
            .IsUnicode(false);

        modelBuilder.Entity<Bebida>()
            .Property(e => e.valorUnitario)
            .HasPrecision(19, 4);

        modelBuilder.Entity<Bebida>()
            .HasMany(e => e.Itens)
            .WithOptional(e => e.Bebida)
            .HasForeignKey(e => e.idBebidas);

        modelBuilder.Entity<Festa>()
            .Property(e => e.local)
            .IsUnicode(false);

        modelBuilder.Entity<Festa>()
            .Property(e => e.data)
            .IsUnicode(false);

        modelBuilder.Entity<Festa>()
            .Property(e => e.status)
            .IsUnicode(false);

        modelBuilder.Entity<Festa>()
            .Property(e => e.valorTotal)
            .HasPrecision(19, 4);

        modelBuilder.Entity<Festa>()
            .HasMany(e => e.GarconsContratados)
            .WithRequired(e => e.Festa)
            .HasForeignKey(e => e.idFesta)
            .WillCascadeOnDelete(false);

        modelBuilder.Entity<Festa>()
            .HasMany(e => e.Itens)
            .WithOptional(e => e.Festa)
            .HasForeignKey(e => e.idFesta);

        modelBuilder.Entity<Garcon>()
            .Property(e => e.nome)
            .IsUnicode(false);

        modelBuilder.Entity<Garcon>()
            .Property(e => e.cpf)
            .IsUnicode(false);

        modelBuilder.Entity<Garcon>()
            .Property(e => e.sexo)
            .IsUnicode(false);

        modelBuilder.Entity<Garcon>()
            .Property(e => e.telefone)
            .IsUnicode(false);

        modelBuilder.Entity<Garcon>()
            .Property(e => e.email)
            .IsUnicode(false);

        modelBuilder.Entity<Garcon>()
            .HasMany(e => e.GarconsContratados)
            .WithRequired(e => e.Garcon)
            .HasForeignKey(e => e.idGarcon)
            .WillCascadeOnDelete(false);

        modelBuilder.Entity<GarconsContratado>()
            .Property(e => e.fone)
            .IsUnicode(false);

        modelBuilder.Entity<GarconsContratado>()
            .Property(e => e.email)
            .IsUnicode(false);

        modelBuilder.Entity<GarconsContratado>()
            .Property(e => e.valorPago)
            .HasPrecision(19, 4);

        modelBuilder.Entity<GarconsContratado>()
            .Property(e => e.status)
            .IsUnicode(false);

        modelBuilder.Entity<Iten>()
            .Property(e => e.valorTotal)
            .HasPrecision(19, 4);

        modelBuilder.Entity<Usuario>()
            .Property(e => e.nome)
            .IsUnicode(false);

        modelBuilder.Entity<Usuario>()
            .Property(e => e.cpf)
            .IsUnicode(false);

        modelBuilder.Entity<Usuario>()
            .Property(e => e.endereco)
            .IsUnicode(false);

        modelBuilder.Entity<Usuario>()
            .Property(e => e.cidade)
            .IsUnicode(false);

        modelBuilder.Entity<Usuario>()
            .Property(e => e.fone)
            .IsUnicode(false);

        modelBuilder.Entity<Usuario>()
            .Property(e => e.login)
            .IsUnicode(false);

        modelBuilder.Entity<Usuario>()
            .Property(e => e.senha)
            .IsUnicode(false);

        modelBuilder.Entity<Usuario>()
            .Property(e => e.aceitoTermos)
            .IsUnicode(false);

        modelBuilder.Entity<Usuario>()
            .Property(e => e.email)
            .IsUnicode(false);
    }
}