After setting up a VM or Virtual Machine on VirtualBox, one often get the Error Message: Failed to Open Session for the Virtual Machine. This message occurs because virtualization is not enabled in your BIOS. Therefore, in order to fix this error, you must reboot your computer and just before the computer is completely rebooted, you should press the Delete, CTRL F1, F4, or F12 keys in order to get into the BIOS menu.
When you get into the BIOS menu, search for Advance CPU or anything of that nature, where you will see something like: Intel Virtualization Disabled; To enable Virtualization, just highlight Intel Virtualization Disabled and choose Enabled by pressing the down arrow on your keyboard, then pressing F10 to save your changes.
This solution will work while running VirtuaBox on a Ubuntu 20.04 host and running Ubuntu 20.04 on top of VirtualBox.