Bit of a long shot.
1. Restart your router
2. Restart the Roku stick
Roku forums are reporting same issues with other apps. Their suggestion is to reboot the device before adding it again.
When you say Roku, i am assuming it's a full blown Roku Player ?
Have you either changed your NOW password or forced a logout on all your NOW devices recently ?
If so, maybe have a read of this linked thread below if you get a similar error message when attempting to sign in on the NOW App.
Also maybe try the Community search box by typing something like Roku sign in or similar.
It is the full blown Roku and I haven't changed my password or forced a logout on my only mobile device.
I only joined Now tv last night and successfully created a account with a valid user name and password and works great on my mobile....its just a shame these credentials will not work when trying to access now tv through Roku on a bigger screen.
Thanks for the thread, I will take a look.
this is ambiguous, it's not clear when you say Roku if you have a roku own branded stick/box or a nowtv branded roku stick/box.
If you have a nowtv branded roku box/stick, you only need to login with your Now credentials.
If you have a roku's own branded box/stick, then you'll need to login twice, one via the initial setup with your roku account credentials and then install the NowTV channel app and login via that using your Now account credentials. Might be worth heading over to the web pages of roku and doing a password reset to recover your account and set a new password and then the same with nowtv (this site).