11.04 Natty – VirtualBox 4.0 Error “Failed to access the USB subsystem”
Fix from Ubuntu for Beginners!
Issue: User Privileges don’t get assigned correctly.
Open ‘Users and groups’.
Click ‘Manage Groups’ and look for the ‘vboxusers’ group.
Enable your account and reboot.
That fixed it for me but you may need this as well:
Users and Groups main window, click your username and then click ‘Advanced Settings’.
Go to the ‘User Privileges’ tab and scroll down to the bottom where you see this option.
Use VirtualBox virtualization solution
Make sure it is enabled. A reboot would be enough to make the error disappear now.