How to fix Windows Update error code 66a

Troubleshooting Expert

July 16, 2018

Are you wondering how to fix Windows update error 66a? Do not worry! The Windows Report team has enlisted working solutions for you.

Windows users who experience Windows Update error code 66a reported PC crashes, slow PC processes, and Windows Update Error Code 66A .NET Framework prompt is displayed.

This error message appear during several instances such as during Windows shutdown/startup, or while .NET framework is running.

However, the reasons for this error include:

Malware or virus infection
Windows registry corruption
Corrupt or incomplete install of .NET framework software.

Meanwhile, we have compiled applicable solutions to fix Windows update error code 66a. You can try out any of the enlisted solutions below to fix the problem.

Looking for the best tools to fix Windows update issues? Here are our top picks.

How can I fix Windows Update error code 66a?

Scan PC for malware
Run SFC scan
Use CCleaner
Run system restore in safe mode
Revert Windows update changes
Reinstall .NET Framework
Rerun Windows update
Perform a clean boot

Solution 1: Scan PC for malware

Some Windows users ignore the warning message and they click on available links in the mail which contains malware.

Meanwhile, the ideal step afterwards is to use remove the malware from your Windows PC by using MalwarebytesAdwCleaner.

This program is a free utility that will scan and remove PUPs from your computer.

Here’s how to download, install, and use MalwarebytesAdwCleaner on your Windows PC:

Download MalwarebytesAdwCleaner at the official website.
Double-click on the download exe file and follow the prompts to complete installation.
After installation, right-click on the MalwarebytesAdwCleaner icon, and then select “Run as administrator” to open the program.
In the MalwarebytesAdwCleaner display, click on the “Scan” button to commence the scanning operation.
After the completed scan, click on the “Clean” button.
Now, click “OK” when prompted to reboot your PC to complete cleaning.

Alternatively, you can run a full system scan on your Windows PC, by using strong antivirus programs such as Bitdefender (World’s Nr.1), Bullguard, Avast, and AVG to remove virus and malwares.

Solution 2: Run SFC scan

System File Checker scans for the corrupt or missing system files and repairs them. Here’s how to run an SFC scan on your Windows 10 PC:

Go to Start > type cmd > right-click Command Prompt > select Run as Administrator.
Now, type the sfc /scannow command.
Wait for the scanning process to complete and then restart your computer. All corrupted files will be replaced on reboot.

In addition, you can also use a dedicated tool, such as Ashampoo Win Optimizer and IOLO System Mechanic to check for system file corruption.

However, if the error prompt persists, you may proceed to the next method.

Working with SFC will be like a walk in the park after you check out this handy guide!

Solution 3: Use CCleaner

Software leftovers, missing DLLs, and invalid Windows registry keys can also cause Windows update error code 66a problem.

Meanwhile, you can use CCleaner to fix your Windows registry and make it error-free.

Here’s how to download, install, and use CCleaner:

Download CCleaner free version or Download CCleaner Pro version.
Install and follow the prompts to complete the installation.
After installation, launch CCleaner, and then click on “Analyze” option.
After CCleaner has finished scanning, click on “Run Cleaner”. Follow the prompts to enable CCleaner fix the Windows registry.

You can also use other third-party registry cleaners. For more information on the best registry cleaners to install, check out our list.

Meanwhile, if you are still getting Windows update error code 66a, you may proceed to the next method.

Learn more about CCleaner by reading our detailed review.

Solution 4: Run system restore in safe mode

Safe mode starts your PC in a diagnostic mode with only basic files and drivers running.

Therefore, you can perform system restore to revert your system back to a point before you get the error message.

Here’s how to do this:

Shut down your PC and turn it on again.
Navigate to the “Run in Safe Mode” option and hit “Enter”.
Go to Start > Type “system restore” and then hit “Enter”.
Follow the prompts to revert back to a certain restore point.
Wait for the process to complete, and then reboot.

Note: System restore does not affect any of your files, documents, and personal data. However, ensure you select a restore point before you experienced Windows Update error code 66a prompt.

But, if you have not created a restore point, you may proceed to the next solution to undo Windows update.

Check out our handy guide to create a restore point in Windows 10 like a pro!

Solution 5: Revert Windows update changes

Here’s how to do this:

Open the Settings app. You can do that quickly by using Windows Key + I shortcut.
When Settings app opens, navigate to Update & Security section.
Select the Recovery from the left pane.
Under the “Go back to the previous version of Windows 10” option, click Get started.
Keep your files and start the resetting procedure.

After uninstalling recent updates, check if the issue still persists.

Solution 6: Reinstall .NET Framework

Reinstalling .NET Framework can also fix Windows Update error code 66a problem.

However, in order to reinstall .NET Framework, you have to uninstall it from Programs and Features, and then install it afterwards.

Here’s how to do this:

Click Start button, and then click Control Panel.
Click Programs and Feature, or Uninstall a Program under the Programs category.
In the list of installed programs, search .NET framework.
Click Uninstall button which appears at the top of the program list and follow the instructions to uninstall .NET framework.
Restart your PC afterwards.
Now, download .NET framework at the official website
Double-click on the executable file and follow the prompts to install .NET framework.

In addition, you may consider downloading several versions of .NET framework most especially the recent one.

Issues with .NET Framework? Solve them like a real technician with our comprehensive guide!

Solution 7: Rerun Windows update

Incomplete Windows update can also result in Windows Update error code 66a problem.

Also, there are instances where the Windows Update process is halted or disrupted by background process.

Therefore, we recommend that you rerun the Windows update; also, you should ensure the update process is completed. This should fix Windows Update error code 66a problem.

Follow these steps to run Windows update:

Go to Start>type “update” in the search box and then click on “Windows Update” to proceed.
In the Windows Update window, check for updates and install the available updates.
After the update is complete, restart your Windows PC.

Solution 8: Perform a clean boot

Software conflicts by .NET framework dependent applications can also cause Windows Update error code 66a. These applications may run in the background whenever you start Windows.

Nevertheless, clean boot starts up your PC devoid of any software conflicts.

Therefore, you have to be logged on as the administrator before you proceed with these steps:

Go to the search box, and then type “msconfig”
Select System Configuration to open the dialog box as below:
Find Services tab, and then select Hide all Microsoft services box
Click Disable all
Go to Startup tab
Click Open Task Manager
Close Task manager then click Ok
Finally, reboot your PC

Windows 10 won’t boot? Nothing to worry about! Check out our guide to solve the issue quickly!

Hope you are able to fix Windows Update error code 66a problem by using any of the enlisted solutions above? Let us know if you have any questions. Feel free to comment below.

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