Error: No session bound to the current HttpContext

Iam trying to call call a method which having an OpenSession but its ending up with an error
"No session bound to the current HttpContext" in CurrentSesions following line

Code:

---

_currentSession = Instance.GetSessionFactory().GetCurrentSession();

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The following is the full code of CurrentSession

Code:

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public static ISession CurrentSession
        {
            get
            {
                ISession _currentSession = null;
                if (System.Web.HttpContext.Current != null)
                {
                    _currentSession = Instance.GetSessionFactory().GetCurrentSession();
                }
                else
                {
                    _currentSession = SessionFactory.OpenSession();
                }
                return _currentSession;
            }
        }

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and this methods are in a class names "WigleSessionManager" and its constructer is the following

Code:

---

private WigleSessionManager()
        {
            Configuration configuration = new Configuration();
            configuration.Configure();
            string[] Files;
            string src = System.Configuration.ConfigurationSettings.AppSettings["ComponentDirectory"];           
            if (string.IsNullOrEmpty(src))
            {
                throw new Exception("System Error: ComponentDirectory key not defined in web.config");
            }
            Files = Directory.GetFiles(src, "*Entities.dll");
            foreach (string Element in Files)
            {
                try
                {
                    Assembly SampleAssembly;
                    SampleAssembly = Assembly.LoadFrom(Element);
                    configuration.AddAssembly(SampleAssembly);
                }
                catch (Exception)
                {

                }
            }
            sessionFactory = configuration.BuildSessionFactory();
        }

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here in sessionFactory object is showing ENtityFetchCount,EntityLoadCount and Entity names all 0...