Registry Cleaner and error in Windows Update.

CCleaner for Windows
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Try turning off (very temporaraly) UAC does it still give this error.

if no turn UAC back on and see if you get the uac prompt instead of the error you are reporting. I assume you are not on a domain computer.

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It may be worth having a try here

http://support.microsoft.com/kb/971058/en-gb

EDIT... Also consider reseting your permissions they may have been altered

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