The log says that you have VT-x enabled in this VM recipe, hence the VM can't run without VT-x and it gives an error saying so. AFAIK this has not changed recently.
VBox.log wrote:00:00:01.477592 Guest OS type: 'WindowsXP'
00:00:01.480662 fHMForced=true - 64-bit guest
64bit guests require VT-x. I suspect you selected the "XP-64bit" template when you installed the OS, or you tried that "longmode" command line tweak that's been discussed recently.
Make sure you don't have a 64bit template selected in <settings>|General|Basic
, and turn off VT-x in <settings>|System|Acceleration