I recently transferred a virtualbox machine from my laptop to my recently reinstalled desktop. The image works fine on my laptop, but when I try to boot it on my new machine, I get dumped to an "EFI Shell" where it asks me about my hard drives rather than booting the machine.
It turns out that as I was messing around with getting the machine to load (due to Virtualization technologies being disabled), I clicked one too many items on the image settings page.
To fix this, go to the "Settings" page for the virtual machine, and click "System". Under the "motherboard" options, be sure that "Enable EFI (special OSes only)" is unchecked. Then click "OK", and try to boot the machine again. The option that was checked is basically how you get into the EFI Interface.