I was just browsing the forums and came across your post. FWIW I've been running CCleaner (latest) on a 5 mo old Win7x64 HP Pavilion, UAC is set to "Always Notify" and have not encountered any problems like you describe. I got my copy from FileHippo's site. No problems running CCleaner at all during this time on my 64bit setup. Maybe you had a bad download or bad install. If you haven't tried it, maybe a mere uninstall/reinstall would resolve this?