Add the full model number and version of the YouTube app.
I see you're read prior replies. Besides here, be sure to call it in. They need your calls to know it's something to ask to be fixed.
When I try to search for some videos, it is showing up in search results but it says UNABLE TO PLAY THE VIDEO. I later realized that these videos/movies may be paid/free but they require on more click (WATCH NOW) to start playing (when you try to run the same movies using computer). But I guess the SAMSUNG's so called SMART TVs are not smart enough to recognize this and prompt the user if he/she wants to pay to watch the movie.
I'm sure some samsung tech will pass the buck to youtube, but it's samsung's duty to complaint such issues to youtube, put some pressure and get them fixed!!!