Microsoft Knowledge Base Article 918342 contains the following introduction:
When you use a "leaked" product key in a Volume Licensing installation to install Microsoft Windows XP or Microsoft Windows Server 2003 on multiple computers, various issues may occur.
Note A "leaked" product key is a product key that is known to be available to the general public.
For example, you may not be able to install Windows service packs, or to automatically obtain updates from the Windows Update Web site. You may experience the symptoms that are described in the following Microsoft Knowledge Base articles when you install a Windows service pack:
326904 Error message: "The product key used to install Windows is invalid"
883254 You receive a "The product key used to install Microsoft Windows may not be valid" error message when you try to install Windows XP Service Pack 2
842196 "The product key used to install Microsoft Windows may not be valid" error message when you try to install a Windows update in Windows Server 2003
This article describes how to change the Windows XP or Windows Server 2003 Volume Licensing product key after a Volume Licensing installation. For this procedure, you can use the Windows Activation Wizard graphical user interface (GUI) or a Windows Management Instrumentation (WMI) script. The Activation Wizard method may be easier. However, you may prefer the script method if you must change the product key for multiple computers.