I had to go to Users & Groups (in Accessories, I believe) and change User settings by adding self to the Groups adm
and, temporarily, to root
and change password. I then Ctrl-Alt-F2 'ed and
sudo passwd root
to add a root password
Just enter the newly created User password at the prompt for the command, then enter the desired UNIX password for root, twice.
It rebooted nicely after doing the above.
Hope this helps! Give another holler if not -- I'll check back later.