From the Microsoft site----
"That means there's significant corruption of your system files - perhaps even the files that are used to run SFC.
Go to Start / All Programs / Accessories / Command prompt and right click on command prompt and click run as Administrator.
While in Command Prompt, type chkdsk /f /r and enter and let it run. It will want to schedule itself to run at the next restart. Answer yes and then reboot to run the program. It will scan and try to fix any corruption or bad sectors on your hard drive and mostly remove that as a potential cause.
If that doesn't work, then please post any repeating error messages from the Event Viewer concerning System File Checker (Start / Control Panel / Administrative Tools / Event Viewer – or typing eventvwr from the command prompt). Here's how to use Event Viewer: http://www.petri.co.il/vista-event-viewer.htm
. Look in the System section.
Lets do a diagnostic test ot two on your hard drive to check for problems: To test your hard drive, check the manufacturer and then get the diagnostic utility from:http://www.techsupportforum.com/hardware-support/hard-drive-support/302602-hard-drive-diagnostic-utilities.html
(and/or get one from your hard drive or computer manufacturer if they have one available – it wouldn’t hurt to try both). If it fails the test, replace it. If it passes the test, then there's probably nothing wrong with it.
If none of the above work or identify the problem, we'll need to do a system repair/upgrade using the genuine Windows Vista Installation Disk (one you own or one you can borrow from ANYONE). Here's the procedure: http://www.vistax64.com/tutorials/88236-repair-install-vista.html
. Although this will not affect your data, settings, or programs, you should still backup your data before starting just to be on the safe side. You may have a lot of updates to re-install (including any service packs you had to remove). If the version on the system came with SP1 or SP2 pre-installed and the disk is an earlier version, then you'll need to make a slipstream disk as follows:http://www.vistax64.com/tutorials/151606-vista-sp1-slipstream-installation-dvd.html
I hope this helps."