Warning after upgrade to Plesk Obsidian: Upgrade failed. To remove this notice, remove the file C:\Program Files (x86)\Parallels\Plesk/var\upgrade\plesk-upgrade-failure.flag from the server

Symptoms

• Warning after upgrade to Plesk Obsidian

  PLESK_WARN: Upgrade failed. To remove this notice, remove the file C:\Program Files (x86)\Parallels\Plesk/var\upgrade\plesk-upgrade-failure.flag from the server

• The following error found in the Plesk installer log C:\ProgramData\Plesk\Installer\autoinstaller3.log:

  CONFIG_TEXT: Error: The installation of the package 'aspnetcore-3.1' failed with code 232. (upgrade: Upgrading Microsoft .NET Core 3.1 - Windows Server Hosting...)
  Not all packages were installed.

Cause

Windows is not up to date.

Resolution

1. Connect to the server via RDP

2. Install all latest Windows updates in Control Panel > System And Security > Windows Updates

3. Reboot the server

4. Install updates once again

Note: Once the update is finished successfully the file C:\Program Files (x86)\Parallels\Plesk\var\upgrade\plesk-upgrade-failure.flag might be safely removed if the warning is still there.