I have a Nook HD+ and have never had problems with the YouTube app. I would suggest shutting the Nook completely down then restarting it. If that doesn't help, you can access the application settings, under Settings, Applications, My Apps, YouTube then clear the cache and data. Next time you start up YouTube it'll be as if you had never run the app before. You can always try moving the YouTube app to the cloud then reinstalling it. If none of these suggestions work, you may want to check the Help option within the app, which'll direct you to their website so you can see if others are having this problem or report this issue.