Hi,
See the sections "How to obtain help..." and "Known Issues" here:
http://support.microsoft.com/kb/954430
How to obtain help and support for this security update
For information about Security updates, visit the Microsoft
Virus Solution and Security Center for resources and tools to keep your PC safe and healthy. If you are having issues with installing the update itself, visit
Support for Microsoft Update for resources and tools to keep your PC updated with the latest updates.
Also read carefully this article:
http://support.microsoft.com/kb/941729/
"Security updates for Microsoft XML Core Services 4.0 Service Pack 2 may repeatedly appear in the update list on Microsoft Update or on Windows Update".
Hope this helps,
Vincenzo Di Russo
Microsoft® MVP Windows Internet Explorer, Windows Desktop Experience & Security - Since 2003.
My MVP Profile:
https://mvp.support.microsoft.com/profile/Vincenzo