I need help with updating my system. I have downloaded an update for Windows Vista but it’s not installing. I get the Error 646 when I try to install this update on my system. Windows is showing that this update has been successfully downloaded on the system and when I try to install it, the system restarts as if it is being installed. But after the loading time, I realize that no update has been installed. The system keeps on showing that the update has failed to install. I first came across this issue on 12th of December 2008, and since that day I have been unable to update my system. Please help me update my Windows!