For about a week now Windows Update on my work machine has failed to download or install the latest security patches. I've tried Automatic Updates and going directly to the windowsupdate.microsoft.com site, but both methods start to download and then fail with no error messages. Perfect.

So, I did some digging and found that the update log lives here (in default XP Pro): C:\Windows\SoftwareDistribution\ReportingEvents.log

Scrolling down through this text file I find the 9th column over to show the error number: 80264005

Google then brings up Ali's helpful blog entry: Windows update gives a 80246005 error

Basic rundown: Stop the Automatic Updates service, delete the contents of C:\Windows\SoftwareDistribution\DataStore, restart the Automatic Update service and try the download/install of updates again.

Worked for me. Thanks, Ali.