PHP include error when using classes

I am running wamp on windows and am trying to use a php include, however I keep getting errors like so:

Warning: include(class.DB_Functions.php): failed to open stream: No such file or directory in C:\wamp\www\ysc\Clients.php

Warning: include(): Failed opening 'class.DB_Functions.php' for inclusion (include_path='.;C:\php\pear') in C:\wamp\www\ysc\Clients.php

Fatal error: Class 'DB_Functions' not found in C:\wamp\www\ysc\Clients.php

Things I have tried:

• Using include, require_once and require
• Set file and folder permissions to everyone
• with and without class. prefix
• manually setting the include path
• hard coding the entire path

Here is one of the files causing the error (on the include statement line)

   <?php

    include 'class.DB_Functions.php'; 
    $db = new DB_Functions();
    $clients = $db->retrieveClients();

    echo json_encode($clients);

    ?>

One of the php files I cannot include

<?php
class DB_Connect {
    private $conn;

    // Connecting to database
    public function connect() {
        require_once 'Config.php';

        // Connecting to mysql database
        $this->conn = new mysqli(DB_HOST, DB_USER, DB_PASSWORD, DB_DATABASE);

        // return database handler
        return $this->conn;
    }
}
?>

All files are in the same folder where the PHP files that are not classes work fine, but none of the class php files will include.