some systems have configured that you cannot login on non-secure terminals as "root". Usually networked-terminals are considered not secure, and so root login on them is denied. To prevent hackers from learning that they have the correct password, the error message shown is the same as for a bad password.
Check /var/log/auth.log for more info about why a login was denied.
Check for "permitrootlogin" in /etc/ssh/sshd_config (or whatever it's called).
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