VirtualBox can't operate in VMX root mode.

[george_v_reilly]

Host = Vista 32-bit SP1 on a Quad-Core Intel box.
Guest = Kubuntu 8.04

This guest OS worked on this host last week.

I turned it on today and first got an error about VRDP, which I worked around by setting it to port 3391. (I don't think I changed Vista's Remote Desktop settings since last week, but, anyway...)

Now I'm getting the following error as soon as I start the guest OS:

VirtualBox can't operate in VMX root mode.
VBox status code: -4011 (VERR_VMX_IN_VMX_ROOT_MODE).

Result Code:
E_FAIL (0x80004005)
Component:
Console
Interface:
IConsole {d5a1cbda-f5d7-4824-9afe-d640c94c7dcf}

Note: VTX is disabled in the Advanced Settings.

General
Name: Kubuntu Hardy
OS Type: Ubuntu
Base Memory: 512 MB
Video Memory: 8 MB
Boot Order: Floppy, CD/DVD-ROM, Hard Disk
ACPI: Enabled
IO APIC: Disabled
VT-x/AMD-V: Disabled
PAE/NX: Disabled

Hard Disks
IDE Primary Master: Kubuntu Hardy.vdi [Normal, 8.00 GB]

Remote Display
VRDP Server Port: 3391

[sandervl]

Some other piece of software has turned on VT-x. VirtualBox can't operate safely that way, hence the refusal to start.

[george_v_reilly]

Ah! The other piece of software would be Virtual PC 2007. If I have a VPC VM already running, I get the VBox VMX error.

On the other hand, if I start the VBox VM first, Virtual PC starts its VM without complaint. Based on your comment, I'm not sure if that's safe, but it hasn't fallen over yet.

[sandervl]

I would advise against running any two virtualization programs at the same time. VT-x and AMD-V complicate matters.

[phasemaster]

I had exactly the situation that George described, namely all of a sudden seeing the "VirtualBox can't operate in VMX root mode" error when starting a VM and finding out later that this was due to a running Virtual PC instance.

I think it's perfectly ok to ask for not having two virtualization programs running at the same time. All I would kindly like to request is to replace the error message with a more user friendly one, probably hinting towards closing any other running VM systems? I think this would add to one of the core values of VirtualBox, namely having a user friendly and intuitive interface.

[aryan]

Try disabling kvm module...
"modprobe -r kvm_intel" with root privileges. This worked for me...

[stinkly]

Thanks. That certainly worked for me on Fedora 12, 2.6.31.5-127.fc12.i686.PAE, and is a lot more pleasant option than recompiling the kernel, which I haven't had to do since I was a little girl.