I'm developing a website with ASP.NET MVC, NHibernate and Fluent Hibernate and getting the error "no session or session was closed" when I try to access a child object.

These are my domain classes:

public class ImageGallery {
    public virtual int Id { get; set; }
    public virtual string Title { get; set; }
    public virtual IList<Image> Images { get; set; }
}

public class Image {
    public virtual int Id { get; set; }
    public virtual ImageGallery ImageGallery { get; set; }
    public virtual string File { get; set; }
}

These are my maps:

public class ImageGalleryMap:ClassMap<ImageGallery> {
    public ImageGalleryMap() {
        Id(x => x.Id);
        Map(x => x.Title);
        HasMany(x => x.Images);
    }
}

public class ImageMap:ClassMap<Image> {
    public ImageMap() {
        Id(x => x.Id);
        References(x => x.ImageGallery);
        Map(x => x.File);
    }
}

And this is my Session Factory helper class:

public class NHibernateSessionFactory {
    private static ISessionFactory _sessionFactory;
    private static ISessionFactory SessionFactory {
        get {
            if(_sessionFactory == null) {
                _sessionFactory = Fluently.Configure()
                    .Database(MySQLConfiguration.Standard.ConnectionString(MyConnString))
                    .Mappings(m => m.FluentMappings.AddFromAssemblyOf<ImageGalleryMap>())
                    .ExposeConfiguration(c => c.Properties.Add("hbm2ddl.keywords", "none"))
                    .BuildSessionFactory();
            }
            return _sessionFactory;
        }
    }
    public static ISession OpenSession() {
        return SessionFactory.OpenSession();
    }
}

Everything works fine, when I get ImageGallery from database using this code:

IImageGalleryRepository igr = new ImageGalleryRepository();
ImageGallery ig = igr.GetById(1);

But, when I try to access the Image child object with this code

string imageFile = ig.Images[1].File;

I get this error:

Initializing[Entities.ImageGallery#1]-failed to lazily initialize a collection of role: Entities.ImageGallery.Images, no session or session was closed

Someone know how can I fix this?

Thank you very much!