If you see this video https://www.youtube.com/watch?v=UKY3scPIMd8 in your YouTube app’s video feeds, your device is affected. (Note: If the video appears unexpectedly in a web browser, it means that website is using an outdated method to access YouTube videos.)

As we upgrade the YouTube Data API to bring more features, we’ll begin shutting down the old version on April 20, 2015. This will result in the current YouTube app not working on certain device models from 2012 and older.

We will continue to focus our efforts on improving our official YouTube app for TV which is available on most 2013 and newer Smart TVs and Blu-ray players, game consoles, streaming devices, and set-top boxes (e.g. Virgin Media, BSkyB Now TV Box, TiVo). You can find a list of our device partners here.

How can I continue using YouTube on affected devices?

Source: https://support.google.com/youtube/answer/6098135?hl=en