Windows Update error 8007066A or 66A

If you receive Windows Update error 8007066A or 66A, it means that Windows has found corrupted files on your PC while trying to install updates to Microsoft .NET Framework 4 Client Profile. Follow these troubleshooting steps to address this problem. If one method doesn't work, try the next.

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Repair the .NET Framework installation

To repair the Microsoft .NET Framework 4 Client Profile installation, follow these steps:

  1. Close any programs that are currently running.

  2. Click the Start button Picture of the Start button , click Control Panel, and under Programs, click Uninstall a program.
  3. In the list of programs, double-click Microsoft .NET 4 Client Profile.

  4. Select Repair .NET Framework 4 Client Profile to its original state, and then click Next.

  5. After the repair is complete, click Finish, then click Restart Now to restart your computer.

  6. Open Windows Update, and try to install the update again.

Fix MSI software update registration corruption issues

An automatic troubleshooter is available that fixes some problems with Windows Update, and it might resolve this error for you.

  1. Click this button:

    Picture of a Fix it button

    Fix this problem

  2. Click Run, and then follow the steps in the wizard.

  3. Open Windows Update, and try to install the update again.

Advanced troubleshooting

If the problem still persists after you've followed these steps, see this Windows Update error article on the Microsoft Support website.

Error codes this applies to:

  • 8007066A

  • 0x8007066A

  • 66A

  • WindowsUpdate_8007066A

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