Why does my WPDB enquiry on test server work but not on the live server?

I am using wordpress to output some ads on a non wordpress page. The HTML on the non wordpress test server page is:

<?php
require('/home/mcreativ/public_html/parts/imagerotator/wp-load.php');
echo init_ads();
?>

On my Test server I have this code in the functions file and the post type is a custom post type I have created call manufacturer:

function init_Ads() {
echo $_SERVER['DOCUMENT_ROOT'];
$serial = $_GET["serial"];
        // args for query
        $args = array(
            'numberposts' => -1,
            'post_type' => 'manufacturer',
            'meta_key' => 'smashing_post_class',
            'meta_value' => $serial
        );
$the_query = new WP_Query( $args );
$the_query->the_post();
$meta= get_post_meta( get_the_ID(), 'ad_rotator_group', TRUE); 

wp_reset_query();  // Restore global post data stomped by the_post().

echo adrotate_group($meta);
}

And on the test URL http://www.m1creative.org/noword/index.php?serial=57 it works.
I am passing in a number ‘serial’ and extracting its corresponding ad group which then displays the correct ads on the page. Use serial = 57 to get a valid ad group.

On the live server page: https://www.partslocator.com.au/adsrotator/testnoword.php?serial=57 it doesn’t work.

This is the HTML of the live server non wordpress page:

<?php
require('/var/www/plm/data/www/partslocator.vm-host.net/adsrotator/wp-load.php');
echo init_ads();
?>

If I change the echo adrotate_group($meta); to echo adrotate_group(1); I get the correct result and the ads display.

I am not using the loop in the query as there is only ever going to be one result.

Is the https causing me problems or is there something else I haven’t spotted?