On hosts which have upgraded from 13.0 to 13.1, the virtualbox driver gives the following error:
VBoxHeadless: Error -1908 in suplibOsInit!
VBoxHeadless: Kernel driver not installed
VBoxHeadless: Tip! Make sure the kernel module is loaded. It may also help to reinstall VirtualBox.
With the September quarterlies, and Virtualbox version 6.1.36, you will need to remove the driver and uninstall Virtualbox, then reboot.
kldunload vboxdrv
pkg delete -f virtualbox-ose virtualbox-ose-kmod
Now reboot, and log back in as root.
pkg install -y virtualbox-ose virtualbox-ose-kmod
kldload vboxdrv
mkdir -p /etc/vbox
mkdir -p /usr/local/etc/vbox
echo "* 0.0.0.0/0" > /usr/local/etc/vbox/networks.conf
ln -s /usr/local/etc/vbox/networks.conf /etc/vbox/networks.conf
service vboxnet restart
The packbox and startvms commands should work fine now.