Windows XP Update Failed After Refresh Install (upgrade on top of existing system)

In this CNET Forum Post , you can find a very simple and effective solution to Windows Update Failed problem.

I had some problem with my Windows XP instance. After a refresh install (reinstall Windows XP using upgrade option); the Windows Update reports fail to apply updates. There is no obvious reason. I had this problem several times before. After lots of search, I finally come across this effective and simple solution.

Windows XP updates fail to install

by fnlvn2 - 28/07/07 00:16
In reply to: Windows Update KB928366 by jackfrost64

This sounds like a problem that I have after I've performed a repair installation. It's taken me about 6 months of research through tech sites including Microsoft's to find a repair that always works. In summary all if my updates would download but, all failed to install.
The solution is to register the dll files associated with the Windows Update Program. To do this do the following
Go to the start button then then the run button and type the following:

regsvr32 wuapi.dll (enter) you will recieve a confirmation message
regsvr32 wuaueng.dll
regsvr32 wuaueng1.dll
regsvr32 wucltui.dll
regsvr32 wups.dll
regsvr32 wups2.dll
regsvr32 wuweb.dll

Reboot and go to the windows update site and try to install your security update. I do understand that my problem was somewhat different than yours. However, one of the items that I was attempting to update was the same as yours. Therefore I'm quite confident that the solution is the same.