This issue appears in systems which boot-up very quickly. This does not give ample enough time for the system to detect that a PowerCore is in your computer.
To avoid this error you can pause the bootup for a short time by pressing the "break" key. The PowerCore will then be recognized. It's also possible to slow down the bootup in the BIOS of your PC.
As nearly every mainboard has a unique BIOS, it is not possible to give a exact description. Please refer to the manual of your mainboard or the manufacturer.
This issue was fixed with PowerCore 1.7 (and upwards) which requires Windows XP, but can still occur with some system configurations with newer PowerCore software versions; make sure you have the latest PowerCore software installed.