virtualbox.org

I am trying to install Ubuntu in a virtualbox VM on my Windows 8.1 computer. I have a Core i7 cpu with VT-X enabled (I checked in the bios and virtualization is enabled)

When I try to boot the ubuntu iso, I get the following error:
Unable to boot. This kernel requires and x86-64 CPU, but only detected an i686 CPU.

I searched on google and on this forum, but could not find a solution.

Did you select the 64 bits OS type in the list?
If you already did, please read Minimum information needed for assistance.

Set the guest OS type to 64-bit or use:

Thank you.