In this scenario we have exported a protected machine to VirtualBox while the host server has the Windows Hyper-V role enabled and is running.
When attempting to run the virtual machine, there is an error on VirtualBox stating "VT-x/AMD-V hardware acceleration is not available on your system. Your 64-bit guest will fail to detect a 64-bit CPU and will not be able to boot".
The root cause for this failure is due to the fact that Windows Hyper-V is running and is controlling access to the VT-x Virtualization Technology capabilities of the host.
When the VirtualBox VM tries to run, VirtualBox is not able to take control of the VT-x Virtualization Technology since Hyper-V has already taken control.
Although it is possible to temporarily prevent the Windows Hyper-V hypervisor from starting at bootup, this method has been known and proven to cause the operating system of the host to crash/BSOD. Therefore this method will not be explained or outlined here.
The safer method to allow VirtualBox to run the exported virtual machine is to remove the Hyper-V server role from the host server. This may require a reboot of the machine but is the best and safest solution.
For additional information on removing server roles, please visit this Microsoft Technet page - https://technet.microsoft.com/en-us/library/cc732257.aspx