Flash not working with YouTube

I updated Flash, Firefox, and Windows 7 on 12/10/14. Since that time I am no longer able to use Flash on YouTube. I get a black player and the message: "An error has occurred. Try again later." I'm using Firefox version 34.0.5 and Flash version 16.0.0.235. If I disable Flash the HTML5 player works. This is a real pain because I'd rather use the Flash player and several other sites I visit require Flash. Anyone have any suggestions on how to fix this? I don't know if the problem is with Flash, YouTube, or Windows. Any help would be appreciated.