Frank's solution didn't work for me too.
But i solved it by uninstalling the .net framework extended and left the .net client on the server.
Update worked after that and the extended component came back with the latest updates.
Windows 7 - Error Code: 66a (Can't install KB2160841)
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Anonymous
Getting error code 66A Windows update encountered an unknown error. Security Update for .NET Framework 4 on Windows XP, Windows Server 2003, Windows Vista, Windows 7, Windows Server 2008, Windows Server 2008 R2 for x64-based Systems (KB2160841)
Installation date: 10/17/2010 2:14 PM
Installation status: Failed
Error details: Code 66A
Update type: Important
A security issue has been identified that could allow an attacker to compromise your Windows-based system that is running the Microsoft .NET Framework and gain complete control over it. You can help protect your computer by installing this update from Microsoft. After you install this item, you may have to restart your computer.
Windows for home | Previous Windows versions | Windows update
Locked Question. This question was migrated from the Microsoft Support Community. You can vote on whether it's helpful, but you can't add comments or replies or follow the question.
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Anonymous
Answer accepted by question author
Anonymous
See Andre.Ziegler reply to an earlier post involving the error:
Answer accepted by question author
Anonymous
had same problem,for a week,go to control panel click uninstall programs,find >Net framework 4 client profile file ,then click right and do repair file ,install part worked fine right after
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Anonymous
2010-11-08T02:51:00+00:00 You're the man. I was researching this problem and your solution was by far the best/easiest thing to do. THANKS !!!