I purchased Avast Internet Security v6 and installed it on my computer using Windows 7. No problems at all. I installed it on my other computer running Windows 7 and I keep getting an error message that says that "an unauthorized change has been made to windows etc. with an error code of 0xC004D401. I uninstalled Avast using their uninstaller and re-installed Internet Security. But the same thing keeps happening. Why would one system be fine and the other have this problem. Both are running the same Windows 7 OS. How do I correct this?