Updates are not installed successfully from Windows Update, from Microsoft Update, or by using Automatic Updates after you repair a Windows XP installation??

I had this problem- so I thought I'd post the fix here.

from Microsoft's website -[SYMPTOMS
When you try to install updates from the Windows Update Web site, from the Microsoft Update Web site, or by using the Automatic Updates feature, you receive a message that states that the update or the updates were not installed successfully. However, the updates are not displayed in the Update History part of the Web site.

You experience this problem if the following conditions are both true:
• You try to update a computer that is running Windows XP.
• You have repaired the Windows XP installation by using the Windows XP CD.

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CAUSE
This problem occurs because of how the Windows XP repair operation replaces Windows system files. When you repair a Windows installation by using a Windows XP CD, the repair operation performs both of the following operations:
• It replaces all the Windows system files with the corresponding files from the CD.

Note This includes the Windows Update files.
• It restores the Windows registry.
The latest version of Windows Update includes a file that was not available in the release version of Windows XP. This file is named Wups2.dll. Therefore, after the repair operation is complete, the following situation exists:
• The Wups2.dll file remains on the computer.
• The registry entries that correspond to this file are missing.
Because the registry files that correspond to the Wups2.dll file are missing, update installations are unsuccessful.]

the fix-

[Method 1: Register the Wups2.dll file in Windows
To register the Wups2.dll file in Windows, follow these steps:

1. Stop the Automatic Updates service. To do this, follow these steps:
a. Click Start, click Run, type cmd, and then click OK.
b. At the command prompt, type the following command, and then press ENTER:
net stop wuauserv
2. Register the Wups2.dll file. To do this, follow these steps:
a. 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

b. Click OK on each verification message that you receive.
3. Start the Automatic Updates service. To do this, type the following command at the command prompt, and then press ENTER:
net start wuauserv
4. Exit the command prompt. To do this type exit, and then press ENTER.]

and more info here-
http://support.microsoft.com/?kbid=943144