I'm running OS X El Capitan 10.11.1 and Windows 10 VM. I just updated Parallels to the newest version this evening. I was running the previous update. This problem has happened twice now a couple of weeks apart. Both times the error started when I tried to save a pdf via Acrobat Reader DC. I clicked the save icon and the screen froze. It didn't matter whether I shut Win10 VM down normally or simply pressed on the power button on my MB Pro. When the VM rebooted, I could hear the sound that Windows loaded but a log in screen never appeared. It obviously didn't fully load as it wouldn't show me the start menu nor would it open IE. I went through this a good six or 7 times. I even thought perhaps I had an outdated version of Acrobat and when I tried to update it told me I was running the most current version. I got very fed up as I lost a couple hours of work and decided to load Bootcamp. It loaded normally. Then I shut down and rebooted OS X and rebooted the virtual machine. It had some adjusting to do as the VM was in a different state as the bootcamp partition. Once it got past that it loaded Windows with some disc errors that the system had to go through. It's now been working fine for 2 days. This is freaking me out as I could have clients in front of me at any given moment and can't have this crap happening. Any advice or wisdom is greatly appreciated.