You will see this error if you are trying to sign-in to PlayStation Network (PSN) with an account that is already bound to another local user. Switch user to sign-in with the correct local user.
If you want to bind your PSN account to a different local user on your PS4, you need to delete the user it is currently bound with and create a new local user - you can't unbind a PSN account from a local user. Go to [Settings] > [Users] > [Delete User] to do this.
Please note that Parental Control settings may stop you from creating new local users.