Scenario 1

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.

Scenario 2

This problem occurs when the latest Windows Update client has been installed and then you install Windows XP SP3 before restarting the computer. This causes the new Wups2.dll file not to be enabled (registered). When Windows XP SP3 is installed, it does not detect the Wups2.dll file, and it sets the registry to point to the original Wups.dll file version that is included in Windows XP SP2 and Windows XP SP3. Because the registry files that correspond to the Wups2.dll file are missing, update installations are unsuccessful.

To resolve this problem, use one of the following methods.

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:
         1. Click Start, click Run, type cmd, and then click OK.
         2. 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:
         1. 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
         2. 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.

Method 2: Download and install the Windows Update Agent
For more information about how to download the latest version of Windows Update Agent, click the following article number to view the article in the Microsoft Knowledge Base:
949104 (http://support.microsoft.com/kb/949104/ ) How to obtain the latest version of the Windows Update Agent to help manage updates on a computer

Reference: http://support.microsoft.com/kb/943144/en-us