A failure in updating could happen when you suddenly get disconnected or downloaded corrupted data which happens a lot. And it seems that there is no local check to ensure that the file is actually complete. It just attempts to install the downloaded material even if its not complete. The stupid thing is that even though you try to update again, it just checks the cache, see that its there and won't bother redownloading the files.
Therefore when you face such a scenario, you could take these steps to solve your problems:
- Open Command Prompt by Start -> Run and type "cmd"
- On the Command Prompt, type "net stop wuauserv". This is done so that you will terminate the windows automatic update service to allow us to delete the cache files
- Still on the Command Prompt, type "cd /d %windir%" or "cd\windows"
- Type "rd /s SoftwareDistribution"
- Thats it, the cache has been purged. Now we need to restart the windows automatic update service again. To do that, type "net start wuauserv"
Or you can use a utility called Temp File Cleaner from ADDPCs.com