Since upgrading to Ubuntu 14.04, When I launch my VirtualBox virtual machine I get:

Failed to open a session for the virtual machine win7pro32bit.

Implementation of the USB 2.0 controller not found!

Because the USB 2.0 controller state is part of the saved VM state, the VM cannot be

 started. To fix this problem, either install the 'Oracle VM VirtualBox Extension Pack'

 or disable USB 2.0 support in the VM settings (VERR_NOT_FOUND).



Result Code: NS_ERROR_FAILURE (0x80004005)

Component: Console

Interface: IConsole {8ab7c520-2442-4b66-8d74-4ff1e195d2b6}

The solution to the same question for 12.10 does NOT fix the problem:

sudo apt-get purge virtualbox

sudo apt-get autoremove

sudo apt-get update

sudo apt-get install virtualbox

UPDATE: Also happens when upgrading VirtualBox itself to 5.0, within existing Ubuntu 14.04.