A Windows XP update pushed out two months ago is leaving some users unable to update their systems.

Microsoft has confirmed that XP users who need to restore their systems after a major crash using the XP recovery disk will no longer have access to the Windows Update service.

"We are aware of an issue where some XP customers are not able to install updates when using the latest version of the Windows Update client and after using the 'repair from CD' function," said a Microsoft spokesman.

The issue occurs because an XP repair CD replaces all system files, including Windows Update, with older versions of those files.

"The most current version of Windows Update includes a file that was not present in the Windows Update image on the CD, so the new file remains on the system after the repair install and this mismatch causes some updates to fail installation," said the spokesman.

A workaround has been published on the Microsoft Help & Support website.