virtualbox.org

The system in question does not install. After booting from the iso file the screen becomes unreadable and I can no longer continue.
Solutions

Which screen becomes unusable? You posted in Linux Hosts, so I can assume you are referring to the host screen?

There has been plenty of recent reports about garbled displays with Ubuntu guests, so I suggest you search for them. The "Linux Guests" forum seems like an obvious place to look.

As a guess I would say it has to do with artifacts on the screen and multi colors.
You can try the following approach and see if it allows you to continue:

Press Host+F1 and speak the phrase "Oh great Spock, fix this screen" then press Host+F7.