@Anonymous User
Welcome to the forum.
First off, just double check on your My Account > My Passes page
http://account.nowtv.com/passes
and make sure your passes are still showing as active there.
The box does very occasionally log out of the NOW TV account, have you checked if this is the case? Open up the NOW TV app on your box, go to the My Account screen from the main menu (if you see any adverts on screen just click through them all) and check that your box is signed in with your username. If not, just click Sign In to do this (if it is signed in, just try a sign out and back in again to see if this solves it).
