Parallels Update Changed Ubuntu Admin User and Password - kb123324 Doesn't Work

A recent Parallels update trashed my Windows 10 and Ubuntu 16.04 VMs. I've almost got Windows 10 fixed but I can't even log on Ubuntu. The admin user account was replaced with "parallels" and the password changed. Haven't managed to guess the new password and can't get into grub as described in KB 123324 (http://kb.parallels.com/en/123324). I'm not sure what the "target" is mentioned in Step 4 of the KB and have not managed to call up the grub menu to get into recovery mode and reset the password for user parallels - the only admin account. It may be that the SSD disk is too fast and I'm missing something.

Anybody have any words of wisdom?

 

I finally managed to get into grub and root. Now when I try to passwd parallels and type and retype a new password, I get passwd: Authentication token manipulation error
passwd: password unchanged

PROBLEM SOLVED - didn't think I needed to remount the filesystem. Failing to do so was the latest problem. Can now log on as user parallels.