MrAndrewMcDonald -
Thank you for posting.
There's a few basic things we'd want to try. First, from the Home screen go to My Games and Apps. Highlight the Xbox Video app's tile, and press the Menu button. Select Manage App from the popup menu. On the next screen it will have some details about the app. Press Menu again, and select Uninstall. When it finishes, power your Xbox completely off by pressing on the Power button (Xbox logo) on the console itself for a few seconds, until it powers off. Then, unplug the power cable for 30 seconds. Basically, these steps are clearing out cached data within the app.
After waiting, plug the console back in again and power it back on. Sign in, and go to My Games and Apps. Xbox Video should still be there, but it'll have to download app data and update.
If this doesn't resolve the issue, I recommend getting in touch with a Live support agent for further troubleshooting:
http://support.xbox.com/en-US/contact-us#0:0:1
Regards,
Kevin J S