Fix Error 0000066A | Windows Update Encountered An Unknown Error

Windows Update fails to install: Security Update for .NET Framework 4. Cannot Install KB2160841 In the following Operating System:

• Windows XP
• Windows Server 2003
• Windows Vista
• Windows 7
• Windows Server 2008
• Windows Server 2008 R2 for x64-based Systems 

Solution:

Try the following steps:

1. Go to Program and Features (on windows vista and later) for earlier version of Operating System, go to control panel and chose Add Or Remove Programs, click it.
2. Scroll down to Microsoft.Net Framework 4 Client Profile, right click it.
3. It will give you a choice of Uninstall/Change, click it.
4. Then, it will give a choice to Repair it, pick Repair it. It will take about 4-10 minutes to repair (with my PC) your experience may vary.
5. When completed, go to your update center, and update it again.

If that doesn't work and if you are someone who is not a computer savy, try this, Remove Microsoft .Net Framework 4.0 with the .NET Framework Cleanup Tool (http://blogs.msdn.com/b/astebner/archive/2008/08/28/8904493.aspx ) , reinstall the Microsoft .Net Framework 4.0 and install the Update.

Reboot your PC.