Blocking is preventing a deviant from commenting to you and your deviations. Before 2017, you were still able to view their profile but unable to watch them, send a note, give anything, comment or favorite while being blocked by the deviant or when you block the deviant.
In 2017, DeviantArt updated their blocking system. Now blocked users can no longer view the deviant's profile and their deviations while being blocked by that deviant or when you block the deviant. Same goes for the Not Found and deactivate error.