composer drupal-update fails / Could not decode JSON: Syntax error

> Drupal\composer_manager\Composer\Command::update
Script Drupal\composer_manager\Composer\Command::update handling the drupal-update event terminated with an exception


  [UnexpectedValueException]
  Could not decode JSON: Syntax error

Exception trace:
 () at D:\InetPub\wwwroot\drupal8\modules\composer_manager\src\JsonFile.php:36
 Drupal\composer_manager\JsonFile::read() at D:\InetPub\wwwroot\drupal8\modules\composer_manager\src\PackageManager.php:75
 Drupal\composer_manager\PackageManager->getExtensionPackages() at D:\InetPub\wwwroot\drupal8\modules\composer_manager\src\PackageManager.php:222
 Drupal\composer_manager\PackageManager->rebuildRootPackage() at D:\InetPub\wwwroot\drupal8\modules\composer_manager\src\Composer\Command.php:38
 Drupal\composer_manager\Composer\Command::update() at phar://C:/ProgramData/ComposerSetup/bin/composer.phar/src/Composer/EventDispatcher/EventDispatcher.php:255
 Composer\EventDispatcher\EventDispatcher->executeEventPhpScript() at phar://C:/ProgramData/ComposerSetup/bin/composer.phar/src/Composer/EventDispatcher/EventDispatcher.php:209
 Composer\EventDispatcher\EventDispatcher->doDispatch() at phar://C:/ProgramData/ComposerSetup/bin/composer.phar/src/Composer/EventDispatcher/EventDispatcher.php:95
 Composer\EventDispatcher\EventDispatcher->dispatchScript() at phar://C:/ProgramData/ComposerSetup/bin/composer.phar/src/Composer/Command/ScriptAliasCommand.php:59
 Composer\Command\ScriptAliasCommand->execute() at phar://C:/ProgramData/ComposerSetup/bin/composer.phar/vendor/symfony/console/Command/Command.php:259
 Symfony\Component\Console\Command\Command->run() at phar://C:/ProgramData/ComposerSetup/bin/composer.phar/vendor/symfony/console/Application.php:844
 Symfony\Component\Console\Application->doRunCommand() at phar://C:/ProgramData/ComposerSetup/bin/composer.phar/vendor/symfony/console/Application.php:192
 Symfony\Component\Console\Application->doRun() at phar://C:/ProgramData/ComposerSetup/bin/composer.phar/src/Composer/Console/Application.php:222
 Composer\Console\Application->doRun() at phar://C:/ProgramData/ComposerSetup/bin/composer.phar/vendor/symfony/console/Application.php:123
 Symfony\Component\Console\Application->run() at phar://C:/ProgramData/ComposerSetup/bin/composer.phar/src/Composer/Console/Application.php:102
 Composer\Console\Application->run() at phar://C:/ProgramData/ComposerSetup/bin/composer.phar/bin/composer:43
 require() at C:\ProgramData\ComposerSetup\bin\composer.phar:25

{
    "name": "drupal/drupal",
    "description": "Drupal is an open source content management platform powering millions of websites and applications.",
    "type": "project",
    "license": "GPL-2.0+",
    "require": {
        "composer/installers": "^1.0.21",
        "wikimedia/composer-merge-plugin": "~1.3"
    },
    "replace": {
        "drupal/core": "~8.1"
    },
    "minimum-stability": "dev",
    "prefer-stable": true,
    "config": {
        "preferred-install": "dist",
        "autoloader-suffix": "Drupal8"
    },
    "extra": {
        "_readme": [
            "By default Drupal loads the autoloader from ./vendor/autoload.php.",
            "To change the autoloader you can edit ./autoload.php."
        ],
        "merge-plugin": {
            "include": [
                "core/composer.json"
            ],
            "recurse": false,
            "replace": false,
            "merge-extra": false
        }
    },
    "autoload": {
        "psr-4": {
            "Drupal\\Core\\Composer\\": "core/lib/Drupal/Core/Composer",
            "Drupal\\composer_manager\\Composer\\": "D:\\InetPub\\wwwroot\\drupal8\\modules\\composer_manager/src/Composer"
        }
    },
    "scripts": {
        "pre-autoload-dump": "Drupal\\Core\\Composer\\Composer::preAutoloadDump",
        "post-autoload-dump": "Drupal\\Core\\Composer\\Composer::ensureHtaccess",
        "post-package-install": "Drupal\\Core\\Composer\\Composer::vendorTestCodeCleanup",
        "post-package-update": "Drupal\\Core\\Composer\\Composer::vendorTestCodeCleanup",
        "drupal-rebuild": "Drupal\\composer_manager\\Composer\\Command::rebuild",
        "drupal-update": "Drupal\\composer_manager\\Composer\\Command::update"
    }
}