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“.