Really annoyed as I have this error on numerous occasions when watching (or trying to watch) a single episode of a programme. Time to cancel subscription me feels.
If you are using either an LG or Samsung Smart TV with the inbuilt NOW App, then have you tried unplugging the power to the television for about 2 minutes to see if that clears the fault.
Should it be a different playback device, then please confirm what you are using.
I won't be much help if your playback device is a PC or Mac because i tend to use streaming boxes or sticks myself and have no experience watching NOW on a PC.