Thank you. My original problem was that System File Checker had found some corrupt files but was unable to repair them. I used the Tweaking.com repair tool with no success in fixing this. A repair install of Windows 7 cured the problem. I noticed during the installation, Windows repaired .NET Framework 4. This may have been the cause of the problem. In which case, repairing .NET Framework 4 may have been the cure for the SFC problem. I will check into that the next time I find a similar problem.