I often have the situation that I get a pre-installed VirtualBox image with some new Oracle stuff to test. Sometimes these images don’t start with this error message:
“This kernel requires an x86-64 CPU, but only detected an i686 CPU. Unable to boot – please use a kernel appropriate for your CPU”
The solution here is not to “Enable Intel VT-x/AMD-V from BIOS”. But this is a necessary option, too.
The solution is to change the setting of the vm before starting and switch it from e.g. “Ubuntu 32bit” to “Ubuntu 64bit”.