I was trying to do something on my wife’s computer and noticed that one of Windows “Important” Updates had failed. As I researched it, I noticed that the update had been trying but Failing to install for over a year.
I looked for a solution, and one thing I did was this.
Ctrl Panel – Windows Updates – View Update History – Installed Updates
From there, I did a search for KB266 and found that it had already been installed in May of 2012. Why it was trying to download and install again was obviously the problem. I then selected that update and chose uninstall. Once it uninstalled, I went back to regular Windows Update and installed the same update and it installed correctly.
While you may not have this particular update problem, if you follow the same path, it may help you fix future update failures.