What playback device are you using ?
Have you tried fresh batteries in the remote and then press the back button on the remote and then jump back into the NowTV stream you want to watch.
If that doesn't work, then see if unplugging the power to your device for a minute helps.
I am guessing you tried the Sky Store button trick previously mentioned on here ?
Also from memory this recent error fault effected BT Broadband users who had to enable file sharing on their Router.
I believe this recent error message can be caused if you are also using a third party software such has Ad blockers like Pi - Hole on your Router.
If the remote is not responding to the stick, then maybe try the things in this trouble shooting guide below.
Also does the NowTV Stick respond when using the Roku Remote App on your smartphone ?