When running a Windows XP or 2003 in VirtualBox, under certain circumstances, the guest may generate a BSOD when booting. The message of the BSOD is a:

DRIVER_UNLOADED_WITHOUT_CANCELLING_PENDING_OPERATIONS

It is accompagnied by a referral to processr.sys, intelppm.sys or p3.sys, depending on the CPU used to install the machine.

The reason for this BSOD is a problem with these drivers, trying to perform an unsupported operation inside the virtual machine (like updating microcode or changing the power state of the CPU).
The issue usually surfaces when the guest machine is moved to a different  ...