The following errors appears during Plesk upgrade or update:
"Unable to obtain the required version of Plesk Installer: The required version '3.20.17' was not found on the server.
This could happen because of configuration error at the installation source.
The MD5 checksum of the C:\ParallelsInstaller\parallels_installer_Microsoft_6.2_x86_64_3.20.17.exe.tmp file does not match the value specified in the configuration file."
Attempt to download is blocked by Gateway Anti-Virus Service.
Try to download ai.exe manually. Open Internet browser and try to download http://ch.origin.autoinstall-win.plesk.com/Autoinstaller_3.20.17/ai.exe.
If it blocks by Antivirus, please check antivirus settings, make sure that Plesk files are not blocked.