VBox on 14.04, Kernel driver not installed (rc=-1908)
You need to compile some kernel drivers:
First
$ sudo apt-get install build-essential module-assistant
$ sudo m-a prepare
Second, as mentioned in the error, reinstall the kernel module.
sudo /etc/init.d/vboxdrv setup
This should solve your problem.
Sometime only second step can solve your problem (so try it first).
Source: http://www.binarytides.com/fix-vbox-kernel-driver-error/