Error when instantiating Context with Entity Framework

Question

I’m taking the Entity Framework to learn, but when I run my code, it returns the following error:

System.Typeloadexception: 'Inheritance security rules were violated by type: 'Mysql.Data.Entity.Mysqlefconfiguration'. Types should correspond to the safety accessibility of the type of base or be less accessible

Error line:

EntityContext contexto = new EntityContext();

Entitycontext class:

[DbConfigurationType(typeof(MySqlEFConfiguration))]
public class EntityContext : DbContext
{
    public EntityContext() : base("MyContext")
    {

    }

    public DbSet<Usuario> Usuarios { get; set; }

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        base.OnModelCreating(modelBuilder);
        modelBuilder.Entity<Usuario>();
    }
}

App.Config:

<connectionStrings>
  <add name="MyContext" providerName="MySql.Data.MySqlClient"
     connectionString="server=localhost;database=teste;uid=root;password="/>
</connectionStrings>

What could be going on? How to fix?