SFC and unrepairable corrupt files

[speedracer]

Hello all. I am really confused as to what is going on with my computer. I am running Win 7 Ultimate with SP1. I run virus and malware scans and also use the SFC function to ensure file integrity. When I run the SFC /scannow the msg states there were some corrupt files and it was successful in repairing/replacing them. When I reboot and run it again it then says there were corrupt files and it could NOT repair the files. I just tried booting with install disc, repair computer, command promt and then ran SFC again 'offboot'. It comes back and says found corrupt files and successfully repaired. Again, reboot and run again to ensure all is right and it says it found more corrupt files. I can run it several times and never comes back with all files ok just that it repaired and everything should be ok. When I do a normal boot and run SFC normally, the same thing. I ran malware and virus checkers and NO problems reported. SO, what is causing these system files to be reported as bad and IF it says it repaired and was SUCCESSFUL why then when I run it again after a reboot are they still being reported as corrupt when the msg said it was repaired successfully. ANYONE???? I just don't get it.. Thanks for all help rendered...