Unable to update, upgrade or install Plesk: The installation of the package ‘example’ failed with code 1603

Symptoms

Plesk update, upgrade or installation fails with an error that is similar to the following:

Failed to install 'C:ParallelsInstallercachepoolreleasePLESK-WIN_18.0.64_15680dist-windowsplesk-backend.msi': Fatal error during installation. (Error code 1603)
Sub-action 'InstallMsiPackage' failed with error code: 1603(0x00000643)
Error: The installation of the package 'plesk-backend' failed with code 1603. (upgrade: Upgrading Plesk Utilities...)
Not all packages were installed.

Upgrading Plesk base locale...
Failed to install 'C:ParallelsInstallerparallelsPANEL-WIN_17.8.11dist-windowsplesk-locale-base-en-US_mu011.msi': Fatal error during installation. (Error code 1603)
ERROR: The installation of the package 'plesk-locale-base-en-US' failed with code 1603. (upgrade: Upgrading Plesk base locale...)
Not all packages were installed.
Please contact product technical support.
exit status 1

Cause

Another MSI package installation is in progress or a reboot is required after a previously completed installation of an MSI package (many MSI package have such a requirement).

Resolution

1. Connect to the server via RDP

2. Complete the installation of any pending Windows updates

3. Reboot the server

4. Open Windows Task Manager and verify that the msiexec.exe process is not running. In case it is running, either wait for the process to finish or terminate it manually.

5. Restart Plesk update in a command-line interface:
   5.1. Start a command prompt as an Administrator
   5.2. Execute the following command:

   C:> plesk installer update

6. If the installation fails with the same error message, follow the steps from this official Microsoft article:
   MSI installation error 1603 - Windows Server | Microsoft Learn