When I try to open a virtual machine, I get the error: "The VirtualBox Linux kernel driver (vboxdrv) is either not loaded or there is permission problems with /dev/vboxdrv. Please reinstall virtualbox-dkms package and load the kernel module by executing 'modprobe vboxdrv' as root".
But when I execute 'modprobe vboxdrv', I get "could not insert 'vboxdrv':Required key not available." I am using Ubuntu 18.04 LTS.