403 Forbidden error followed by Fatal error:

On phpBB.com home page.
First got the following error;
Forbidden

You don't have permission to access / on this server.

Additionally, a 403 Forbidden error was encountered while trying to use an ErrorDocument to handle the request.

Apache Server at www.phpbb.com Port 443

Followed by:

Fatal error: Uncaught exception 'Symfony\Component\DependencyInjection\Exception\InvalidArgumentException' with message 'The parameter "debug.error_handler.throw_at" must be defined.' in /var/www/phpbb.com/data/write/symfony/app/cache/prod/appProdProjectContainer.php:1220 Stack trace: #0 /var/www/phpbb.com/website-old/symfony/vendor/symfony/symfony/src/Symfony/Bundle/FrameworkBundle/FrameworkBundle.php(50): appProdProjectContainer->getParameter('debug.error_han...') #1 /var/www/phpbb.com/website-old/symfony/app/bootstrap.php.cache(2334): Symfony\Bundle\FrameworkBundle\FrameworkBundle->boot() #2 /var/www/phpbb.com/website-old/symfony/app/bootstrap.php.cache(2362): Symfony\Component\HttpKernel\Kernel->boot() #3 /var/www/phpbb.com/website-old/symfony/web/app.php(25): Symfony\Component\HttpKernel\Kernel->handle(Object(Symfony\Component\HttpFoundation\Request)) #4

thrown in /var/www/phpbb.com/data/write/symfony/app/cache/prod/appProdProjectContainer.php on line 1220