VT-x is being used by another hypervisor

[xplosion]

Hi,
On my Windows 8.1 I have installed 4.3.15 r95286 VirtualBox version.
On my virtual box I created a new WIndows 7 machine. It work fine until yesterday when I change the new antivirus (BitDefender Internet Security 2015).
Now when I try to start the machine I receive an error message:

Details:
Apertura di una sessione per la Macchina Virtuale win7 non riuscita.
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).
Codice 'uscita: E_FAIL (0x80004005)
Componente: Console
Interfaccia: IConsole {8ab7c520-2442-4b66-8d74-4ff1e195d2b6}

I don't have other virtualization programs !
I search on this forum and on the net but I didn't found any solution.
Can help me ?

Thanks

[mpack]

Believe what error messages tell you. Something else is using VT-x.

I would say: disable Hyper-V. If you are correct that you don't have it installed (it's present by default on Win8 Pro builds), then I'd look to see if BitDefender uses the feature.

Also: please don't discuss VirtualBox test builds outside of the discussion thread where you got it. I'm letting this go because the issue is not version specific.

[Erwane]

I've same error with BT Antivirus 2015.

Disabling "active virus control" works fine (permissive option don't)

The exclusion process don't work too.

[mpack]

The BitDefender forum is most likely discussing an entirely different problem. See the discussion "4.3.14 conflicts with anti-virus" which is stickied near the top of the "Windows Hosts" forum.