Hi madchopper,
We are still looking into what is causing the crash to occur when adding a class that derives from UserDefinedEnum. However, in order to remove a code class from a project, you would just need to delete the header and source file for the class (after making sure no Blueprints reference the class and closing the Editor), right-click on the .uproject file and generate project files, then open the solution in Visual Studio and build the project.