What Broni said
It's not SFC that causes the problems that some report...it's their failure to understand that SFC should be run with a disk reflecting either the same SPs (or more recent) and O/S as are currently installed on the system...just as a repair install effort should be.
If I have a system with SP3 installed, I use a disk with SP3 installed to obtain files. If I only have SP2 or SP1 installed on the system...I can use a disk reflecting SP3 or SP2 for sure, but not SP1 or no SP2.
You may want to read, http://www.bleepingcomputer.com/forums/topic43051.html
Worst case...if sfc /scannow installs an older file...that should be overcome easily by just reinstalling the latest SP (SP3), IMO.
Edited by hamluis, 12 June 2011 - 12:42 PM.