Windows Update has an issue where if you didn't install service packs yourself and if you try to get a service pack with Windows Update, the way that Microsoft wants home users to update Windows, then apparently, Windows Update then F-s up, it fails to install service packs before other updates! And thus, apparently, Windows Update keeps trying to install updates without prerequisites and thus Windows Update gives an error! Especially with an update for .Net Framework 3.5, you're probably gonna get a message from Windows Update telling you that it didn't complete and give you an error code! The only solution is to have the service packs installed manually BEFORE running Windows Update!