The controversial silent update that Microsoft deployed widely in
July and August is blocking the "repair" feature of Windows XP from
completing successfully.
Redmond faced a huge backlash when it pushed
the patch onto all users computers without telling them.
According to
Windows Secrets, ever since Microsoft sent out the files users of XP's
repair function have been unable to install the latest 80 patches from
Microsoft. Normally, users who repair XP can easily download and install
the latest patches, however since Microsoft pushed out the patch they cannot
do that.
More here.