When using Mock.CreateLike<> we've found that trying to directly mock anything lower than two layers down on a concrete class (e.g. x => x.Layer1.Layer2.Property == "test") throws a NullReferenceException unless the profiler is enabled. It wasn't clear in the exception or the documentation relating to this method that the real issue was the profiler being disabled, and only by trial and error did we find the solution.