I was receiving errors when trying to run
VMware 64-bit virtual machines. Thinking it was VMware-related, I installed multiple versions with same results. I moved to VirtualBox, but I had the same problems.
VirtualBox listed only 32-bit emulation options.
I realized this has something to do with my own computer settings:
I installed CPU-Z to see if at least that tool detects AMD-V. Now this is very strange: it sometimes detects AMD-V and sometimes it doesn't - different results in different power cycles (if I restart the computer it may detect AMD-V or not).
Here is a screenshot of CPU-Z when AMD-V isn't detected: http://i.imgur.com/zDlwU2p.png
I restart the computer and have different results: http://i.imgur.com/xZXAPOc.png
When CPU-Z detects AMD-V, Vmware and VirtualBox are working correctly, also. Why isn't AMD-V detected consistently at each power cycle? I have to restart the computer until AMD-V is detected which may take several attempts.