[s7p9a2m4]

There were a plague of your type of problem here a long time ago and it was related to the catroot folder in windows. Here is the fix.
http://www.helpwithwindows.com/WindowsXP/troub-08.html

If that dos'nt help try the sfc /scannow command.
http://www.updatexp.com/scannow-sfc.html