Cannot back up to My Book Live via Time Machine since Sierra upgrade

Hi. 've logged in to the drive and it reports that the firmware is up to date. However, since I upgraded my Mac to Sierra today Time Machine will not connect to the My Book Live to perform a backup. I can log on to it via Finder without issue.

Can anyone assist?

Hi. Thanks for the instructions. I have followed them but the drive won’t complete a backup. It just sits there saying “Preparing Backup” even after leaving it for 36 hours.