I was having issues with VirtualBox and Avast. When running any VM I would randomly see a Sad Screen/BSOD with the error SYSTEM_SERVICE_EXCEPTION. I also used the logs to determine the error was Avast DLL's. I had to go into Avast, open the menu, select settings, and select troubleshooting. I shut off (unchecked) Enable hardware assisted virtualization and rebooted. The Sad Screen seems to have gone away but I am still waiting to be certain.
I think the issue is the Windows 10 implementation/hardware implementation of virtualization. You cannot have multiple applications using the VM hardware services (Intel VT-x or AMD-V) at the same time - sharing doesn't work. For example if you have Hyper-V installed VirtualBox will crash with similar errors or not start at all.
I am trying to see if there is a solution since this hinder some sandbox features of avast.