Seems the infamous Logitech Control Center is back to wreak havoc.
They released a 2.4 update on the 20th of November and a week later a “mate error” thread surfaced on the mailing list, I have received a dozen support emails about the problem, and if you look at the comments for LCC at VersionTracker or MacUpdate, you’ll find that a lot of users are reporting problems with this update.
So my advice: uninstall LCC. And on a more general note, if something has worked fine for a year, and it suddenly breaks, consider what you did to alter your system in the last week before you write support, thanks! :)