Have you tried resetting the NowTV Hub router by holding the reset button on the back of the router for about 10 secs, then go into your Sky Q box and reset the Networking settings and try again connecting.
If no joy, then i would jump over to the Sky Community Forum, where the NowTV Hub is a clone of the Sky Q Hub router to see if there is anything over there that can help (perhaps use their forum search feature but instead of NowTV Hub use Sky Q Hub Router with the Sky Q box).
I recently had this issue, I wanted to use WiFi instead of ethernet because I wanted to move the router to a better location. I couldn't connect my SkyQ box to my NowTV hub via WiFi, it wouldn't recognise the WiFi password. After a lot of googling I couldn't find an answer but managed to solve it by trial and error.
What I did was, unplugged the ethernet cable, went into settings on SkyQ (settings-status-network connections) and pressed "Network Setup" then "reset".
When you see the options for what router your connecting to, before you choose, press and hold the WPS button on the router until lights flash. Then press "connect to Sky broadband WiFi"