We appreciate your patience regarding this matter. I understand that you are receiving an error message when trying to access the NBC channel.
Just to clarify, have you followed the steps of restarting your Roku device after removing the channel and before adding the channel back? If yes, I'd recommend reaching out to the channel support directly to report the issue and request additional support. Many channels on the Roku platform are developed and maintained by the channel provider directly, and they'll be able to best assist. If other channels are working correctly, and you only experience this issue on that channel (app), that is likely an indication that the issue lies within that particular channel. In these cases, the channel provider will need to investigate the issue in order to help resolve it.
You can reach NBC support here: https://www.nbc.com/contact-us