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I am trying to install SP1 on a Windows 7 Ultimate box using Windows Update, but it fails with this code: 800F0A09 and no further explanation. I have tried to google that, but I am not getting anything useful back. Windows online help is not useful either...

Any suggestion?

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up vote 2 down vote accepted

According to a german blog article it's a problem with Microsoft Security Essentials or Microsoft Forefront Client blocking the installation/deinstallation process. It advises to update those packages. See also this Microsoft page.

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It was forefront, the hotfix linked here: allowed me to install SP1 fine. Thanks :) – Palantir Mar 14 '11 at 9:35

I accept that the Online Windows Update should work without any problem, but in your case it has not worked. Hope this is not a bug and something to do with Internet download/connection!

I always prefer the Offline Installer, which gives me flexibility to install it at any time or on any number of computers. Give a try with the Offline Installer:

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The hotfix Forefront Client Security Antimalware Update may not work, depending on your version of Forefront. You may try uninstalling forefront, installing sp1 via windows update, and re-installing Forefront afterwards. This worked for me, but the above answer did not.

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