We are trying to write an application that uses the NServiceBus library in a VB.NET environment. We've been stymied by errors similar to the following: Reference required to assembly 'NServiceBus, Version=2.0.0.1071, Culture=neutral, PublicKeyToken=9fc386479f8a226c' containing the implemented interface 'NServiceBus.IMessageHandler`1'. Add one to your project. Our project already includes references to NServiceBus.dll and NServiceBus.Core.dll from the same NServiceBus 2.0 RC2 distribution. Steps to reproduce: Create a new VB Class Library Project (.NET 3.5) Add NServiceBus.dll and NServiceBus.Core.dll as References. Put the following code in Class1.vb: Imports NServiceBus.Sagas.Impl Class Test Public Function Foo() As SagaMessageHandler Return Nothing End Function End Class You should now see the compiler error mentioned above. An identical project written in C# has no compile errors. Any ideas about how to solve this problem? (And, yes, my preferred solution is switching to C#, but no, that's not an acceptable one at the moment.)