Without revealing your email address, give us the exact wording of the error you're getting & we'll try and point you in the right direction. This guide may also help: https://yt.be/help/kQvy
Hmm, odd – are you getting the error when logging in to both desktop and mobile device? Try clearing cache & cookies (https://yt.be/help/Cko1 ) or check the app for any updates and try reinstalling it if there's none. Let us know how it goes.