The main problem is that the recent VirtualBox 5.x series has some major compatibility problems with Windows and/or the anti-virus installed with it. Launching a VirtualBox image could result in a pretty scary error message like:
Error relaunching VirtualBox VM process: 5And it's a "hard" error, blocking the VirtualBox image from even attempting to boot the guest OS. Apparently it's something to do with "Hardened Security" . There's some proposed workarounds but none of the proposed solutions worked for me.
Command line: ......
Worse yet, after installation of VirtualBox 5.x (on a Windows 7 host) and successfully testing my Lubuntu guest image, my TrendMicro anti-virus updated overnight which created the above "Hardened Security" problem --- literally overnight!
The only reliable workaround is to downgrade VirtualBox back to the version 4.3.x series. That's a workaround for the VirtualBox "Hardened Security" problem, but it creates new version compatibility problems between the guest OS and VirtualBox... argh
But I found working workarounds.