VirtualBox: Failed to access the USB subsystem

To fix this error, just add the user name to the "vboxusers" group but the User Accounts manager in Ubuntu 11.10 is quite terrible, too simple to be useful so use a command line to do this instead:-

sudo usermod -a -G vboxusers <user-name>

The other option is to install and run the old Accounts manager.

sudo apt-get install gnome-system-tools
users-admin

Refs
http://www.liberiangeek.net/2011/10/add-users-to-existing-groups-in-ubuntu-11-10-oneiric-ocelot-2/
http://linux-software-news-tutorials.blogspot.com/2011/11/restore-old-account-manager-in-ubuntu.html