No session bound to the current context

Question

Friends, I have the following problem, when compiling my application it returns me the 

following error: No session bound to the current context. I use NhibernateHelper, and 

the error appears in this line of code:

public static ISession GetSessao()
       {
           return Instance.GetSessionFactory().GetCurrentSession();
       }
Como posso resolver esse erro?

Segue meu código completo:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using NHibernate.Mapping.Attributes;
using NHibernate.Cfg;
using NHibernate;
using System.IO;
using NHibernate.Context;

namespace SDPJDominio.DataAccess
{
    public class NhibernateHelper
    {
        private ISessionFactory sessionFactory;

        public static ISession GetSessao()
        {
            return Instance.GetSessionFactory().GetCurrentSession();
        }

        public static ISessionFactory Teste()
        {
            MemoryStream stream = new System.IO.MemoryStream();
            HbmSerializer.Default.Validate = true;
            HbmSerializer.Default.Serialize(stream, System.Reflection.Assembly.GetExecutingAssembly());
            stream.Position = 0;
            Configuration configuration= new Configuration();
            configuration.Configure();
            configuration.SetProperty("connection.connection_string", ConfigNhibernate.getConfig());
            configuration.SetProperty("current_session_context_class", "thread_static");
            configuration.AddInputStream(stream);
            stream.Close();

            Instance.sessionFactory = configuration.BuildSessionFactory();
            return Instance.sessionFactory;
        }

        public NhibernateHelper()
        {
            MemoryStream stream = new System.IO.MemoryStream();
            HbmSerializer.Default.Validate = true;
            HbmSerializer.Default.Serialize(stream, System.Reflection.Assembly.GetExecutingAssembly());
            stream.Position = 0;
            Configuration configuration= new Configuration();
            configuration.Configure();
            configuration.SetProperty("connection.connection_string", ConfigNhibernate.getConfig());
            configuration.AddInputStream(stream);
            stream.Close();

            sessionFactory = configuration.BuildSessionFactory();
        }

        public static ISessionFactory SessionFactory
        {
            get { return Instance.sessionFactory; }
        }

        private ISessionFactory GetSessionFactory()
        {
            return sessionFactory;
        }

        public static NhibernateHelper Instancia
        {
            get
            {
                returnCreateSessionKey.gerenciadorDeSessao;
            }
        }

        public static ISession OpeningSession()
        {
            return Instance.GetSessionFactory().OpenSession();
        }

        public static void ReloadSession(object obj)
        {
            CurrentSession.Refresh(obj);
        }

        public static ISession ReloadSession
        {
            get
            {
                return Instance.GetSessionFactory().GetCurrentSession();
            }
        }

        class CreateSessionKey
        {
            internal static readonly NhibernateHelper SESSIONMANAGER= new NhibernateHelper();
        }
    }
}
Could you kindly help me?