NHibernate on Mono running ASP.NET MVC 3 web application

I am having issues with NHibernate on Mono (Ubuntu server 13.04)

Mono version:

Mono JIT compiler version 3.2.1 ((no/f3f789e Wed Aug 21 17:40:25 UTC 2013)
Copyright (C) 2002-2012 Novell, Inc, Xamarin Inc and Contributors. www.mono-project.com
    TLS:           __thread
    SIGSEGV:       altstack
    Notifications: epoll
    Architecture:  amd64
    Disabled:      none
    Misc:          softdebug
    LLVM:          supported, not enabled.
    GC:            sgen

I get this exception:

System.InvalidProgramException
Invalid IL code in System.Data.Common.DbProviderFactories:GetFactory (string): method body is empty.

Details:

Non-web exception. Exception origin (name of application or object): NHibernate.

Exception Stack Trace:

at NHibernate.Driver.ReflectionBasedDriver..ctor (System.String providerInvariantName, System.String driverAssemblyName, System.String connectionTypeName, System.String commandTypeName) [0x00000] in <filename unknown>:0 
at NHibernate.Driver.NpgsqlDriver..ctor () [0x00000] in <filename unknown>:0 
at (wrapper managed-to-native) System.Reflection.MonoCMethod:InternalInvoke (System.Reflection.MonoCMethod,object,object[],System.Exception&)
at System.Reflection.MonoCMethod.InternalInvoke (System.Object obj, System.Object[] parameters) [0x00000] in <filename unknown>:0 

The code where I get the exception looks like this:

    protected void Application_Start()
    {
        AreaRegistration.RegisterAllAreas();

        RegisterGlobalFilters(GlobalFilters.Filters);
        RegisterRoutes(RouteTable.Routes);

        //NpgsqlEventLog.Level = LogLevel.Debug;
        //NpgsqlEventLog.LogName = "NpgsqlTests.LogFile"; 

        SessionFactory = Fluently.Configure().Database(FluentNHibernate.Cfg.Db.PostgreSQLConfiguration.Standard.
            ConnectionString(c =>
                c.Host("localhost")
                .Database("newtest")
                .Username("postgres")
                .Password("******")
                .Port(5432)
            )).Mappings(m =>
            m.FluentMappings.AddFromAssemblyOf<Entity>())
            .ExposeConfiguration(c => c.SetProperty("current_session_context_class", "web"))
            .BuildSessionFactory();
    }