Today I ran into a computer where windows update would download updates from Windows Update and would start the installation process before finally failing to install any of the updates. No reason was given for the failure. Looking at the update history, where one would expect to find the error, did not even have the update attempt listed.

First, where to find more information about the errors related to Windows Update: c:\windows\WindowsUpdate.txt. You might find some clues regarding the problems there. I Google'd on a couple of errors listed there and found the following solution for the problem I was experiencing.

Solution (re-register these dlls):

regsvr32.exe c:\windows\system32\wuweb.dll
regsvr32.exe c:\windows\system32\wups2.dll
regsvr32.exe c:\windows\system32\wups.dll
regsvr32.exe c:\windows\system32\wucltui.dll
regsvr32.exe c:\windows\system32\wuaueng1.dll
regsvr32.exe c:\windows\system32\wuaueng.dll
regsvr32.exe c:\windows\system32\wuapi.dll

Next, restart the Automatic Updates server (you might have to reboot to get Windows Update working in IE).

This problem was on an XP system for me but I have heard this also affects other Windows OS's.