Fix Microsoft Security Essentials Upgrade Error 0X80070645

If your installation of Microsoft Security Essentials is corrupted, or if you have problems running the uninstall wizard, Microsoft Windows may not remove references to antivirus software from the registry.

If MSE has not been removed properly, an error may occur when trying to reinstall the application or use another antivirus program, leaving your workstation unprotected. You can edit the registry and remove all relevant keys and values ​​to manually uninstall Security Essentials.

To resolve this issue, you must perform one of the following solutions:

Remove Microsoft Security Essentials

First, you need to uninstall Microsoft Security Essentials, remove any remaining registry subkeys, and then manually install the latest version of Microsoft Security Essentials.

To do this, follow these steps.

  • In the search box, click Start, type or copy and paste Appwiz.cpl and press Enter.
  • Right-click Microsoft Security Essentials and select Uninstall.
  • Restart your computer.
  • If you managed to uninstall Microsoft Security Essentials using the previous steps, see Step 4. Reinstall Microsoft Security Essentials. If you are unable to uninstall Microsoft Security Essentials and some of the Microsoft Security Essentials components have not been removed, you may not be able to reinstall Microsoft Security Essentials.

If you cannot uninstall Microsoft Security Essentials using Add or Remove Programs or Programs and Features, follow Step 2: Register the registry and Step 3: Delete the Microsoft Security Essentials registry subkey. Step 2: Save the recording

Clear the Microsoft Security Essentials Tracking Registry

Delete the following registry key:

  • HKEY_CLASSES_ROOT> Installer> Update Codes> 26D13F39948E1D546B0106B5539504D9

Then, when you reinstall Microsoft Security Essentials, you may find that it doesn’t update the first time, but everything is fine after reboot.

Restart Windows in Safe Mode

From Windows:

  • Press Windows logo key + I on your keyboard to open Settings.
  • If that doesn’t work, click the Start button in the lower left corner of your screen, then select Settings.
  • Select Update & Security> Recovery.
  • In the Advanced Startup section, select Restart Now.
  • After the computer restarts, on the Select an option screen, select Troubleshoot> Advanced options> Startup options> Restart.
  • After restarting your computer, you should see a list of options. Select 4 or F4 to start your computer in Safe Mode. If you need to use the Internet, select 5 or F5 for Safe Mode with network drivers loaded.

On the login screen:

  • Restart your computer.
  • At the login screen, hold down the Shift key while choosing Power> Restart.
  • After the computer restarts, on the Select an option screen, select Troubleshoot> Advanced options> Startup options> Restart.
  • After restarting your computer, you should see a list of options. Select 4 or F4 to start your computer in Safe Mode. If you need to use the Internet, select 5 or F5 for Safe Mode with network drivers loaded.