ResolutionStarting from 10.3, Parallels Installer for Windows installs micro-updates when upgrading to the new version, and is able to execute code snippets embedded into each micro-update. Parallels Plesk Panel 10.2 or earlier does not include the new Installer. Therefore, earlier versions are unable to install micro-updates during the upgrade.
To successfully perform the full upgrade, you need to first download the latest version of the Installer from the official Parallels site, and perform the upgrade procedure using it. You can download the installer from the following link: http://download1.parallels.com/Plesk/PP10/10.3.0/Windows/parallels_installer.exe.