Folks still rocking some of the original Google TV devices — such as the Logitech Revue and Sony’s Google TV box — will find themselves out of a YouTube app the next time they go to use their devices. Google has moved on to using their newest YouTube APIs, and only those who can update to certain recent versions of the YouTube app will be supported.
The problem is that many of the devices that haven’t moved on from Google TV software versions 1 and 2 have no way of getting a more recent version of the app. As such, they’ll either need to upgrade to newer devices or use the HTML5 version of YouTube from their web browser. It’s unfortunate, but that’s the sort of stuff you often have to deal with if you aren’t interested in upgrading.
You can check which version of Google TV your device has by heading to Settings > Customer Support > Android Version. If you have 3 or 4, great — head to Google Play and make sure you have the latest YouTube update. Otherwise you should probably start thinking about your options for upgrading to something more contemporary.