I installed a Lubuntu 16.04 LTS (and a v.17) both architectures x86 and 64 bits.
The problem is when I shut down the Virtual Lubuntu (installed) then, sometimes runs ok but one of them, the machine shows how is starting Lubuntu, but only shows an black screen. I can't do anything. I tried several times and I got always the same problem.
It was working fine the same machine I was working since 1 month and I never get this problem...