Password problems (root)

Hi,

I've recently installed Virtualmin on a fresh Ubuntu 16.04 VM. At a certain point in the installation docs, it mentions setting a root password for Webmin for Ubuntu systems and using that root user to administer Virtualmin. I could not get the command to work though. All I got was the usage help screen.

root@host1:~# /usr/{share,libexec}/webmin/changepass.pl /etc/webmin root password
usage: changepass.pl <config-dir> <login> <password>
 
This program allows you to change the password of a user in the Webmin
password file. For example, to change the password of the admin user
to foo, you would run:
        changepass.pl /etc/webmin admin foo
This assumes that /etc/webmin is the Webmin configuration directory.

So I sudoed to root, and set a password via passwd. Now i could log in to Virtualmin, and finish the installation. The problem is, on next boot I could no longer login to Virtualmin using the same user / pass credentials. Figured out the changepass.pl thing though:

root@host1:~# /usr/share/webmin/changepass.pl /etc/webmin root password
Updated password of Webmin user root

But still no luck trying to login to Virtualmin. What's going on here?