Magento – Magento 2.1.2 error 500

This error has nothing to do with Plesk it's from the Magento script itself. Whoever wrote it clearly has no idea of PHP OOP. Sorry but it's true.

There's nowhere to be found an "use" keyword in the script but you can clearly see that he's trying to use

  Cli

class without specifying the namespace. That's the whole error if you change it to

  Magento\Framework\Console\Cli

it will work.

Change the bin/magento shell file from:

#!/usr/bin/env php
<?php
/**
 * Copyright © 2013-2017 Magento, Inc. All rights reserved.
 * See COPYING.txt for license details.
 */

if (PHP_SAPI !== 'cli') {
    echo 'bin/magento must be run as a CLI application';
    exit(1);
}

try {
    require __DIR__ . '/../app/bootstrap.php';
} catch (\Exception $e) {
    echo 'Autoload error: ' . $e->getMessage();
    exit(1);
}
try {
    $handler = new \Magento\Framework\App\ErrorHandler();
    set_error_handler([$handler, 'handler']);
    $application = new Magento\Framework\Console\Cli('Magento CLI');
    $application->run();
} catch (\Exception $e) {
    while ($e) {
        echo $e->getMessage();
        echo $e->getTraceAsString();
        echo "\n\n";
        $e = $e->getPrevious();
    }
    exit(Cli::RETURN_FAILURE);
}

to

#!/usr/bin/env php
<?php
/**
 * Copyright © 2013-2017 Magento, Inc. All rights reserved.
 * See COPYING.txt for license details.
 */

if (PHP_SAPI !== 'cli') {
    echo 'bin/magento must be run as a CLI application';
    exit(1);
}

try {
    require __DIR__ . '/../app/bootstrap.php';
} catch (\Exception $e) {
    echo 'Autoload error: ' . $e->getMessage();
    exit(1);
}
try {
    $handler = new \Magento\Framework\App\ErrorHandler();
    set_error_handler([$handler, 'handler']);
    $application = new Magento\Framework\Console\Cli('Magento CLI');
    $application->run();
} catch (\Exception $e) {
    while ($e) {
        echo $e->getMessage();
        echo $e->getTraceAsString();
        echo "\n\n";
        $e = $e->getPrevious();
    }
    exit(\Magento\Framework\Console\Cli::RETURN_FAILURE);
}

Take a look at the exit at the end...

Sorry if I offended somebody ;]

Removed your var/generation directory and var/cache directory.

You need to remove it manually, if it is ubuntu then locate in your magento 2 root directory and run rm -rf var/generation and rm -rf var/cache command.

Then try to run below commands in sequence.

• php bin/magento setup:di:compile
• php bin/magento setup:upgrade
• php bin/magento cache:clean
• php bin/magento cache:flush