It is difficult to diagnose the problem based upon the information provided. Here are a few recommendations:
1) Unplug your TV and/or streaming device for 30 seconds. Cycling the power will “reboot” the device, often resolving any problems caused by extended use.
2) Delete the YouTube TV app and reinstall it. If any of the program code has been corrupted during the update process, a fresh install will resolve it.
3) If still not working, please provide more complete details about your problem. Include the hardware that you’re using (TV model, streaming device, etc.) and the exact steps you are performing which lead up to the error. Posting a photograph of the screen with the error displayed is also useful.