Update 2/26/2011: I neglected to mention that this fix is normally only needed for Windows XP. Windows 7 appears to have some auto-fix thing built-in, and I’ve never had this issue with Windows Vista.
I’ve often run into an issue where a Windows update is downloaded but can’t be installed. No matter how many times I tell it to install the update, Windows Update just says that the update failed. Very frustrating.
Luckily, I stumbled upon a solution, and it is so very simple:
Hope this helps someone. Or at the very least it will help me when I run into the issue again in a few months.