windows 7 - Why do I get "this CPU is not compatible with 64-bit mode" on a 64-bit processor?

I have a 32-bit Ubuntu 10.10 as a host OS, VirtualBox 4.0, Windows 7 64-bit Professional as a guest OS. The laptop processor is 64-bit. When I try to load Windows 7 64-bit in VirtualBox, the error appears:

attempting to load a 64-bit application, however this CPU is not compatible with with 64-bit mode

I don't understand, the CPU is compatible with 64-bit mode, what's the problem?

Answer

I believe it's telling you VirtualBox's virtual CPU, though, is not 64-bit compatible. Is hardware virtualization enabled, and have you enabled VirtualBox's 64-bit support for the specific VM in question?

http://www.virtualbox.org/manual/ch03.html#intro-64bitguests

You need a 64-bit processor with hardware virtualization support (see the section called “Hardware vs. software virtualization”).

You must enable hardware virtualization for the particular VM for which you want 64-bit support; software virtualization is not supported for 64-bit VMs.