Ticket #4053 (closed defect: obsolete)

That shouldn't matter. The grayed setting should be disabled in your case but you should be able to start a VM anyway, aren't you?

That actually means that you don't have AMD-V. Minor annoyance.

Hi, I have a similar problem but with an Intel CPU. I have an Intel Core2Duo T5450. It doesn't support VT, but VirtualBox detects end enables it. I cannot uncheck the checkbox, because it's grayed out. My guest OS (Win 7) starts, but after 2 minutes, seems nothing to be happen, i think it's extremely slow.

CPU reference:  http://www.intel.com/products/processor_number/chart/core2duo.htm This topic says guest OS-es are faster when VT-X is disabled on processors doesn't support it:  http://forums.virtualbox.org/viewtopic.php?f=2&t=13720&start=15

VirtualBox version: VirtualBox-2.2.4_47978_fedora11-1.i586

I'm having the same problem. The guest had run without issues on a Ubuntu x86-32 host. Later it was moved (the whole .VirtualBox directory was copied) to an Ubuntu x86-64 host that has VT-X support. The guest ran there, also without problems.

Now I've moved .VirtualBox back to the x86-32 machine, and the guest cannot be started. The checkbox for the VT-X option (along with nested paging) is checked and greyed out. When I try to start the guest I get:

Failed to start the virtual machine WinXP_Pro.
VT-x is not available. (VERR_VMX_NO_VMX).
Unknown error creating VM (VERR_VMX_NO_VMX).

FWIW, I'm using 3.0.12. I tried to change the machine's XML without progress. There are two <Hardware>/<CPU> tags in it, one under the single <Snapshot> tag and one directly under <Machine>. The one under <Snapshot> was already "correct":

<CPU count="1">
  <HardwareVirtEx enabled="false"/>
</CPU>

The one under <Machine> however looked like this:

<CPU count="2">
  <HardwareVirtEx enabled="true"/>
  <HardwareVirtExNestedPaging enabled="true"/>
</CPU>

However, after changing it to look like the first <CPU> tag, the guest still shows up with VT-X and nested paging enabled and greyed out in the VB window! Where else are these settings stored?

Please reopen if this is still a problem with a recent VirtualBox release.