Windows 7 + PhysX

I just did a clean install of Windows 7 Ultimate 64-bit on my dev machine, with the new 195.62 drivers. By default, PhysX is disabled – and when I run the DeviceQueryDrv SDK example, it runs just fine (though only showing 2 GPU’s when I have 2x GTX295’s in the system). If I enable PhysX, then run the device query again, it freezes for a couple of seconds before running and showing 3 GPUs (still not 4 though!).

Just curious, why does it freeze when PhysX is enabled, but not when it’s disabled?