Windows update loops, and will not install downloaded files.
This is a common issue if you have configured or turned on certain settings in Internet Explorer. Below are the steps to walk through and resolve this issue with your settings.
* Launch Internet Explorer
* Click on the “Discussion” icon to disable this feature
* Close Internet Explorer

MORE FIXES:
Errors Occur When You Try to Install Updates from the Windows Update Web Site
The information in this article applies to: Microsoft Windows XP Professional & Microsoft Windows XP Home Edition

SYMPTOMS
When you use the Windows Update Web site to install updates, you may receive a 643 error message or a message indicating that Windows Update was unable to complete the operation.


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