faratian's suggestion helped a family member on a MacBook with this issue i.e. disabled "Share screenshots using Dropbox" under the Import tab in Dropbox Preferences and then rebooted
In another case on a MacBook Air (macOS Mojave v10.14.6), closing VLC and iMovie solved the issue as well.
As others have mentioned, this does appear to an issue prevalent only in the last few months but I've not read any official response from NowTV tech support to confirm or otherwise if this is indeed a safeguarding measure they have introduced.
I certainly did not experience this in the previous football season 2018/19 having often had the NowTV player playing in the background whilst working on iMovie projects for example.
Don't really know why you called me out, I was first marginally involved in this thread nearly a year ago. The guys in this thread had a problem with utilities running in the background of their OSes which they had to either delete or prevent from running, more than that I do not know or hold any further interest it.
Therefore, if you still have a problem with your Now TV app then contact their Help Text Chat.
The information you provided was inaccurate. I wanted you and anyone else who came across your post after searching for help with the error to know that and so avoid unnecessarily alarm. Don't be upset. It's not personal, it's educational.