Hi. Just upgraded to 3.1.0.
I cannot start my Win XP VM with existing settings as VirtualBox 3.1.0 claims VT-x not detected.
I used it for a long time on my ThinkPad T61p with T7500 processor (see support in Intel doc: http://ark.intel.com/VTList.aspx
Ok, playing with settings some more: This happens when I select 2 Processors, which seems to be legal (green bar).
Switching back to 1 processor the VM starts fine.
Something is wrong here - Either it is not possible to assign 2 processors to Win XP guests with a dual core host processor (which the settings show as fine) or VT-x detection is broken.
Let me know if I can provide more info to help. Thanks.