After a recent kernel upgrade, I found my VirtualBox 2.0 stopped launching VMs, and would just sit there with a dialog saying "Spawning Session" and a progresss bar which never went past 0%.
A quick look on Ubuntuforums and I found others are having the same problem. Turns out the kernel module hasn't loaded. We can force a recompile with this command:
sudo /etc/init.d/vboxdrv setup
It then stops, recompiles, and starts the module:
* Stopping VirtualBox kernel module
* Recompiling VirtualBox kernel module
* Starting VirtualBox kernel module
And VirtualBox is working again!