I saw in another post that someone recommended completely removing HWMonitor.app with a software removal tool (I don't remember which one they suggested) and then rerun Multibeast to reinstall it. In my case, I had moved HWM from /Applications to /Applications/System Utils (I like to keep apps categorized, I also have Video Tools and Audio Tools folders - what can I say, I have a touch of OCD), so I ended up with two versions of HWM installed. Once I got rid of the old one (and fixed the Login Items entry for it) everything works.