I had above error message when irritating to install Microsoft Security Essentials on a Windows XP laptop and also a Windows Vista Home Premium laptop or computer. Lastly build out to there were it seems that loose ends of a earlier Microsoft Security Essentials beta series on my laptop. Which had not been uninstalled totally? I used a merchandise identify My Uninstaller to confiscate these remains and series then install. I could not get extra remove program to eliminate all traces of this program. Would advise that Microsoft offer uninstaller software for Microsoft Security Essentials that totally removes all traces of the program from the registry.