If you have upgraded from Windows 7, you may need to also run delmigprov.exe accompanying the standalone version of that update.

…let alone the main executable of a popular open source development tool.

It looked as if it could not propagate an environment variable pointing to the location of the file with my VMs settings to the VirtualBox command-line interface, so the latter kept looking for it in the system profile directory. Worked around by copying the file there; now have a small Ubuntu server running quietly in the background.