Prestashop 1.7 Fresh Install Error: Uncaught Error: Call to a member function getAttributeNS()

[Albatrosss]

Hello. I wanted to set up a prestashop for the subdomain of the website where I use Prestashop. I downloaded prestashop version 1.7.6.8 to clean install. There was no problem until I installed it. But after installing Prestashop, I cannot enter the store. I can log into the back office without any problems. But I can not login to the site. php.ini and .htaccess settings were made. I could not understand what is wrong.

Error:

Notice: Undefined property: DOMDocument::$documentElement in /home2/x/su.x.com/vendor/symfony/symfony/src/Symfony/Component/DependencyInjection/Loader/XmlFileLoader.php on line 579

Fatal error: Uncaught Error: Call to a member function getAttributeNS() on null in 

/home2/x/su.x.com/vendor/symfony/symfony/src/Symfony/Component/DependencyInjection/Loader/XmlFileLoader.php:579 

XML is active in phpinfo ().

Everything is suitable in prestainfo. My main domain is already working normally. But there is such a problem in my sub domain. How can I solve it?

Edited November 4, 2020 by Albatrosss (see edit history)