As a tip, I always make a backup of my .VirtualBox folder and copies it as is into the new system, so no need for a new activation from ms and all is set to run. Of course for this to work your .VirtualBox has to fit on your external, but you can copy one single machine if size is a problem. Btw my #5.1 should be named /etc/udev/rules.d/11-vboxdrv.rules!