NMock2 RemotingException ByRef value type parameter cannot be null

OK this might be the most misleading error message I've seen. I cannot decide on how to describe it... What this means... or what this try to ...
Actually this happens when one of your mocked objects is mocking a method that returns something and your mocking doesn't return anything. Eeeeh - that was quite tricky. Got it?
Here is an example:
When I mock this method:

Public Class FacadeObject 
     Function CreateSomeThing(ByVal aName As String) As Long
               End Function

        End Class

by using the following code to do the mock 

Expect.Once.On(m_mockadFacadeObject).Method("CreateSomeThing")

an exception of RemotingException (ByRef value type parameter cannot be null) will be thrown.
Here is another description that you might find easier to understand