While Microsoft said the “stealth install” of updated Windows update files — even when users had disabled automatic updating — which we wrote about earlier, was harmless, it turns out it wasn’t quite that simple. For XP users, if you happened to do a “repair” using a repair CD, you would no longer be able to use Windows update … period.
The basic reason for this was that the aforementioned stealth update replaced certain Windows update files. When a repair is done, that file is replaced, and Windows Update is no longer able to function. Nate Clinton, program manager for Windows Update, said on the Windows Update blog:
Here’s what we found: when an XP repair CD is used, it replaces all system files (including Windows Update) on your machine with older versions of those files and restores the registry. However, the latest version of Windows Update includes wups2.dll that was not originally present in Windows XP. Therefore, after the repair install of the OS, wups2.dll remains on the system but its registry entries are missing. This mismatch causes updates to fail installation.
I was confused at first, but what he means is the registry entries for the new wups2.dll are missing — I think. BTW, this is the same Nate Clinton who initially said the stealth update was harmless. 
How do you fix it? There’s a Microsoft KB article on it, KB943144. Unfortunately, while people like you and I won’t have issues with the procedure, it’s certainly nothing most users would be comfortable with.
RESOLUTION
To resolve this problem, register the Wups2.dll file in Windows. To do this, follow these steps:
- Stop the Automatic Updates service. To do this, follow these steps:
- Click Start, click Run, type cmd, and then click OK.
- At the command prompt, type the following command, and then press ENTER:
net stop wuauserv- Register the Wups2.dll file. To do this, follow these steps
- At the command prompt, type the following command, and then press ENTER:
regsvr32 %windir%\system32\wups2.dll
Note: For a computer that is running Windows XP Professional x64 Edition, type the following command, and then press ENTER:
regsvr32 %windir%\syswow64\wups2.dll- Click OK on each verification message that you receive.
- Start the Automatic Updates service. To do this, type the following command at the command prompt, and then press ENTER:
net start wuauserv- Exit the command prompt. To do this type exit, and then press ENTER.
We Say: This just goes to show why why it is important that Microsoft shouldn’t force undocumented updates upon users — though I will admit that if a notification popped up with an update centered around Windows Update, I most likely would have downloaded and installed it anyway. 
