After upgrading to PHP 7 or higher you may encounter the following error:

==========================
General Error
SQL ERROR [ mysql4 ]

mysql_connect function does not exist, is mysql extension installed? []

An sql error occurred while fetching this page. Please contact an administrator if this problem persists.
=============================

The reason for this is the mysql request is deprecated in the new version of PHP, as part of the security update to 7 from 5.6.40. All that needs to be done is to modify the configuration file and switch the configuration file from “mysql” to “mysqli” as the method for requesting the database.