The site is currently offline due to encountering an error.

Greetings,

I am getting the following when I navigate to my mautic installation:
The site is currently offline due to encountering an error. If the problem persists, please contact the system administrator.
System administrators, check server logs for errors.

My server logs show the following error entries:

[24-Dec-2018 15:27:21 UTC] Symfony\Component\DependencyInjection\Exception\InvalidArgumentException: The parameter “debug.error_handler.throw_at” must be defined. - in file /home/webfolder/public_html/mauticfolder/app/cache/prod/appProdProjectContainer.php - at line 3510
[24-Dec-2018 15:29:36 UTC] Symfony\Component\Config\Exception\FileLoaderLoadException: Class \Mautic\PluginBundle\Entity\Addon does not exist in /home/webfolder/public_html/mauticfolder/app/config/config.php (which is loaded in resource “/home/sgadmin/public_html/eme/app/config/config.php”). - in file /home/webfolder/public_html/mauticfolder/vendor/symfony/config/Loader/FileLoader.php - at line 122
[24-Dec-2018 15:32:37 UTC] Symfony\Component\Config\Exception\FileLoaderLoadException: Class \Mautic\PluginBundle\Entity\Addon does not exist in /home/webfolder/public_html/mauticfolder/app/config/config.php (which is loaded in resource “/home/sgadmin/public_html/eme/app/config/config.php”). - in file /home/webfolder/public_html/mauticfolder/vendor/symfony/config/Loader/FileLoader.php - at line 122

Your assistance is highly appreciated to resolve this issue. Thank you in advance.

Best regards,
Angelo.