this exact thing happened to me a month or so ago. Out of the blue, nothing changed from the day before. Turned out to be waves licence issue. If you have waves (I have a few v9 go to plugins) this might be the place to start looking.
To be honest, I have no idea how I fixed it. I uninstalled, re-installed. It may have been due to the licence being on a USB drive. I moved the licence to the computer and that may have done the trick…