Corrupt filesystem due to improper shutdown (I know, this is Windows and it never happens)
From eventid.net folks
http://www.eventid.net/display.asp?eventid=13568&eventno=1743&source=NtFrs&phase=1
From the horse:
http://support.microsoft.com/kb/887303
From others (mostly reprints from the horse)
http://www.chicagotech.net/troubleshooting/evenyid13568.htm
http://www.chicagotech.net/troubleshooting/non-authoritativrrestore.htm