public static void ActivateApp(){
    //FB.Init (true);
    FB.ActivateApp();

}

ActivateApp ();

NullReferenceException: Facebook object is not yet loaded.  Did you call FB.Init()?
FB.get_FacebookImpl () (at Assets/Facebook/Scripts/FB.cs:28)
FB.ActivateApp () (at Assets/Facebook/Scripts/FB.cs:272)
MenuManager.ActivateApp () (at Assets/Scripts/Menu/MenuManager.cs:48)
MenuManager.Start () (at Assets/Scripts/Menu/MenuManager.cs:63)