[Newbies] Dealing with AnObsoleteC3 Class

I'm trying to refactor a piece of code using the refactoring browser, but I've started getting messages telling me that AnObsoleteC3 class does not understand #directlyDefinesMethod.

I assume that a changeset I've loaded has removed a class called C3, but that there's still some reference to it hanging around. I guess I need help with two things: - how do I track this thing down? - how do I kill it?

I've inspected 'self' from the debugger, and had a poke around some of the pointer tools, but don't really know what I'm doing. Can anyone enlighten me?