The following message is found in
Failed to install 'C:\\ParallelsInstaller\\parallels\\PANEL-WIN_11.5.30\\dist-msi-Microsoft-2003-i386\\plesk-site.msi': Another installation is already in progress.
Complete that installation before proceeding with this install. (Error code 1618)
One or more
msiexec.exe processes are still running or hung.
Use Process Monitor and Process Explorer to find running or hanging
Kill the found
msiexec.exeprocesses via Task Manager;
Try to upgrade Plesk again.