SymptomsA Plesk upgrade from version 9.3. to version 9.5 fails with this error:
Error: Failed to connect to the licensing server.
ERROR: Failed to check whether a new license key is available.
CauseThe error is caused by autoinstaller and the newest system openssl and curl libraries update.
With the new openssl and curl libraries, it is not possible to retrieve the license key.
ResolutionPlease use the parameter ignore-key-errors for autoinstaller in order to upgrade Plesk to the latest version.
$PRODUCT_ROOT_D/admin/sbin/autoinstaller --select-release-latest --upgrade-installed-components --ignore-key-errors