Reduced performance state is 0 seconds, so it’s not really an error message.
If you don’t want to receive this event then simply turn off its support in BIOS.
1) Enter BIOS by pressing F9 on POST
2) Navigate to “Power Management Options” => “Advanced Power Management Options” => “Minimum Processor Idle Power State”
3) Choose “No C-States”
This alert comes from the byproduct of new Processor Power Management feature in Windows Vista and Windows Server 2008. For more info on this click here