In order to run a 64bit Virtual Machine Operating System on VirtualBox such as Ubuntu 64bit you need to have "Enable VT-x/AMD-V" set within the system setting in VirtualBox but to support that you need to have the system virtualisation hardware support enabled within your BIOS, however, it's normally disabled.
If your Intel Virtualisation / VT-x/AMD-V is disabled then you will get an error similar to this, if you are getting this error and have Gigabyte dual UEFI 3D BIOS then simply follow the instructions below to fix the problem:
Then if you haven't been to the BIOS before, you will be presented with the below screenshot, if you have you may need to navigate to the 3D BIOS to continue. Click on the highlighted area of the 3D Motherboard for DUAL BIOS Setup.
NB: Please be careful, although this change shouldn't have any negative effect on the integrity of your system setup it cannot be guaranteed, all due care has been taken to ensure the information here is correct for the specific BIOS and Software problem explained.