I determined that I was causing my problems - This thread is about what you need to do to make a Modlr plugin, in addition to that, you must also register your custom Ocl class at runtime. Adding [EcoOclOperation(typeof(OclEven), true)] to my EcoSpace solved my problems.But, then this got me thinking. My model is what is dependant on this custom Ocl class, not my EcoSpace. I have 2 EcoSpaces, one for runtime that connects to a database, and one for Unit Tests that utilizes memory. Why should I have to attribute both of these classes? In a perfect OO world, I should attribute my model shouldn't I? Then, each of my EcoSpaces would pick it up because the connect to the same model.