after upgrading to 11.10 i could start virtualbox, but could not start any VMs. i received an error stating the “vboxdrv” kernel module was not running. when i tried to load the module manually i got an message saying the module wasn’t found.

i ended up doing a reinstall of the virtualbox-dkms package and everything was fine after that.

update 5/5/2012: i had to repeat this process after the upgrade to ubuntu 12.04…so perhaps it is safe to assume this needs to be done after every upgrade.