This cause behind this error is installed programs interfering with the Windows Update process. It could be an anti-virus program, or a malware, or a PUP. The reason could also be missing files in the system.

Windows Update Install Error 0x80070020

1] Clear contents of SoftwareDistribution & catroot2 folders

The procedure to clear the contents of the SoftwareDistribution folder is as follows: Search for Command Prompt in the Windows search bar and right-click on the option. Select Run as administrator. Type the following commands and press Enter after each of them to execute them: The first command stops the Windows Update Service and the second command stops the Background Intelligence Transfer Service. Now open File Explorer and browse to the following path: Here C: is the system drive. Select all the files in the SoftwareDistribution folder and hit Delete. In case it doesn’t delete all the files, restart the system and try again. Open an elevated Command Prompt once again as explained earlier. Now type the following commands and press Enter after each command to execute them: This will restart the Windows Update Service and Background Intelligence Transfer Service which we stopped earlier. Next, you have to reset the catroot2 folder. Once you have done this, try and see if it helps.

2] Use the Windows Update Troubleshooter

At times, the Windows Update troubleshooter could be helpful in fixing Windows Update problems. It will clear the Windows Update related temporary files, clear the contents of the Software Distribution folder, repair and reset Windows Update components, check the status of Windows Update-related Services, check for pending updates and more. Here’s the procedure to run the Windows Update Troubleshooter. Click on the Start button and then the gear-like symbol to open the Settings page. Go to Updates and security and then to the Troubleshoot tab. Select the Windows Update Troubleshooter and run it. Restart the system and see. You could also use Microsoft’s online troubleshooter for Windows updates. and see if that helps you.

3] Manually Reset Windows Update components

Reset Windows Update components manually and see if that helps you.

4] Disable the anti-virus software temporarily

One of the reasons behind the issue is that a 3rd party program, usually an anti-virus interferes with the Windows update process. Try disabling your anti virus software temporarily.

5] Install in  Clean Boot State

You could perform a Clean Boot and then run Windows Update. That is known to have helped many.

6] Restart the Windows Update Services

Open the Service Manager and ensure that they are Started and their Startup type is as follows:

Background Intelligent Transfer Service: ManualCryptographic Service: AutomaticWindows Update Service: Manual (Triggered)

Hope this helps!