VirtualBox - VT-x is being used by another hypervisor

OS: Windows 7 x64

VirtualBox: 4.3.14 & 4.3.15

CPU: i5-3570

Motherboard: Gigabyte GA-H77M-D3H

I receive the error below when I try to run a virtual machine with Enable VT-x/AMD-V on. With this setting off the virtual machine runs successfully.

Failed to open a session for the virtual machine
MachineName

VT-x is being used by another hypervisor.
(VERR_VMX_IN_VMX_ROOT_MODE).

Virtualbox can't operate in vmx root mode. Please close all other virtualization programs.
(VERR_VMX_IN_VMX_ROOT_MODE).

I have the virtulization settings set to on in BIOS.

I tried updating BIOS, it didn't fix the problem.

When my BIOS was updated virtulization was off by default, and going into VirtualBox the Enable VT-x/AMD-V option wasn't there, I turned virtulization back on and the option was back - so VirtualBox appears to correctly know when my virtulization is on.

I tried updating VirtualBox from 4.3.14 to 4.3.15 as apparently it fixes some problems with anti-virus programs intefering with VirtualBox, so I updated to rule that out, still the same problem.

I have no other virtulisation software installed as far as I know.

As far as I know I don't have any programs running in compatibility mode.

Any ideas what else could be causing this error? Or is there any way to find out what else is using VT-x?

Solution 1:

It's happened to me when I was using a Android Virtual Device. Check if you are using other virtual machine at the same time.

Hope this help.

Solution 2:

If you have Microsoft Virtual PC installed, or its replacement Hyper-V, you need to uninstall it. Either of these will cause the problem you are seeing.

You may also need to uninstall any other virtualization programs you may have downloaded, such as VMware Player/Workstation.