Hi Sophie, Hi Ben,
thanks! This issue is because until recently Squeak used ContextPart and MethodContext as the class names for contexts, while Pharo had changed to just using Context. Now Squeak trunk is using Context too the compatibility package isn't needed. I've updated the load script to eliminate CogCompatibility.st as you two both did. That's pushed to github. I'm also committing versions of VMMaker and Cog that no longer use the deprecated includedSubString:, so the builds should work less noisily now.
Sophie, welcome! I for one would love to know what your plans with VMMaker are.