Plex Not Loading My Libraries???

I'm running Plex on a Sky NowTV box and, overall, it's been ok, bar the odd time when it won't show my libraries which has been cured by switching off and on again. However, as of yesterday, when I turn my box on It won't load my tv and movie libraries. It was working fine a couple of days ago, i've made no changes, it just won't load them and switching off and on has no effect.
My Plex account and libraries are running on a Macbook Pro. I've tried reconnecting with a new pin, which shows up on the box as connected, but won't load the libraries. I'm still running El Capitan, but it was working fine on this a couple of days ago, but I have the new system ready to update, but can't see that this is the cause of the problem.
The libraries are present on my plex account and the box shows up on my devices, but the libraries won't display on the box. I've tried creating new libraries and they still won't show on the box.
Has anyone else experienced this and/or do you have a solution?