I am receiving "Error code 0000066A Windows Update encountered an unknown error" when Windows Update fails to install: 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). I have tried to manually install the update and it is blocked from installing. I then have tried to uninstall .NET Framework 4 and reinstall it, and that fails as well. I cannot uninstall .NET Framework 4 and I cannot reinstall or update it. What is the solution?