Microsoft Genuine Advantage – Diagnostic Site
Handy site to see if Internet Explorer (a plugin for Firefox available too) is configured correctly to run the validation process.

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0x80080008 error with Windows Update:

net stop wuauserv
regsvr32 wuapi.dll
regsvr32 wuaueng.dll
regsvr32 wuaueng1.dll
regsvr32 wucltui.dll
regsvr32 wups.dll
regsvr32 wups2.dll
regsvr32 wuweb.dll
regsvr32 MSXML3.dll
net start wuauserv


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