YouTube website had recently been updated since few weeks ago, and almost all youtube downloaders have stopped working after that update. I use a mobile YouTube video downloading app, which had stopped working too. Luckily the app developers noted the issue and they released an updated version only after which I could download videos again. So I must say all old youtube video downloading programs may not work anymore unless they're updated or new youtube video downloading apps can fix the issue.
I'm not sure what browser you are working with but the firefox addons still work.
Internet explorer sucks anyway, so dump it for something good, if your one of the few unenlightened ones still using IE.
In Firefox you can add a little addin to keep the web sites thinking your using internet explorer too if you want.
Youtube has been doing this crap for a long time, I get a little "You need to upgrade your browser" bit, I just click no and I'm still good to go.
Let them try to keep people from doing what they want, they can't and won't be able to do it, someone out there will find the info and fix the new great BS and put the fix out for the world to use.