Comment 38 for bug 246067

As everyone said before, this problem is relative to the VT-x / AMD-V setting.

This setting is relative to hardware virtualization support either by your CPU and, as lylepratt wrote, your motherboard. You can find more information about Intel Virtualization Technology (Intel VT) and AMD Virtualization (AMD-V) supported CPUs on the Hardware support section of this Wikipedia x86 virtualization page (http://en.wikipedia.org/wiki/AMD-V).

Activating this option on an hardware which don't support it (CPU and/or motherboard) will not change anything and you will not be able to boot any of these three first alpha.

As found on the Ubuntu KVM Wiki page (https://help.ubuntu.com/community/KVM): To see if your processor supports one of these, you can run the following command. If nothing is printed, it means that your CPU doesn't support hardware virtualisation. Otherwise, it does - but you still need to make sure that virtualisation is enabled in the BIOS.

egrep '(vmx|svm)' /proc/cpuinfo

For information, I'm running Hardy 8.04.1 AMD64 and VirtualBox 1.6.2 on an AMD Athlon 64 X2 3800+ (no AMD-V support).