Never mind - I used the troubleshooting option and unchecked both of the Use Original boxes, and now it works again.
Overall this application is indispensable. I use it to apply -15 through -20dB preamp on some headsets that have misconfigured volume in their drivers. It worked flawlessly up until about two weeks ago when Windows updated. Now, despite restarting, and despite the editor telling me that it updated the registry, the preamp gain has no effect on the output volume. I really hope I can get this working again.