Estou dando continuidade do curso de C#, fiz a aplicação conforme está no vídeo:

program.cs
using Loja.Infra;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Loja
{
    class Program
    {
        static void Main(string[] args)
        {
            NHibernateHelper.GeraSchema();

            Console.Read();
        }
    }
}
-----------------------------------------------------
Usuario.cs
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Loja.Entidades
{
    public class Usuario
    {
        public virtual int Id { get; set;}
        public virtual string Nome { get; set; }
    }
}
-------------------------------------------------
Usuario.hbm.xml
<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" 
  assembly="Loja" 
  namespace="Loja.Entidades">    
    <class name="Usuario">  
        <id name="Id">
            <generator class="identity" />
        </id>
        <property name="Nome" />
    </class>
</hibernate-mapping>
-------------------------------------------------------------
hibernate.cfg.xml
<?xml version="1.0" encoding="utf-8" ?>
<hibernate-configuration xmlns="urn:nhibernate-configuration-2.2">
  <session-factory>
    <property name="connection.driver_class">NHibernate.Driver.MySqlDataDriver</property>
    <property name="connection.provider">NHibernate.Connection.DriverConnectionProvider</property>
    <property name="dialect">NHibernate.Dialect.MySql5Dialect</property>
    <property name="connection.connection_string">
      Server=localhost;Database=loja;Uid=root;Pwd=vini1428;
    </property>
    <property name="show_sql"></property>
  </session-factory>
</hibernate-configuration>
--------------------------------------------------------------------
NHibernateHelper.cs
using NHibernate.Cfg;
using NHibernate.Tool.hbm2ddl;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Reflection;
using System.Text;
using System.Threading.Tasks;

namespace Loja.Infra
{
    public class NHibernateHelper
    {
        public static Configuration RecuperaConfiguracao()
        {
            Configuration cfg = new Configuration();
            cfg.Configure();
            cfg.AddAssembly(Assembly.GetExecutingAssembly());
            return cfg;
        }

        public static void GeraSchema()
        {
            Configuration cfg = RecuperaConfiguracao();
            new SchemaExport(cfg).Create(true, true);
        }
    }
}

Após rodar o projeto aparece o erro:

An unhandled exception of type 'NHibernate.MappingException' occurred in NHibernate.dll

Additional information: Could not compile the mapping document: Loja.Mapeamentos.Usuario.hbm.xml

Em view Detail: O campo NHibernate.MappingException = {"Could not compile the mapping document: Loja.Mapeamentos.Usuario.hbm.xml"}