problem with $wpdb

Hi, I’m using $wpdb in my theme files, (a custom Thematic child theme), and everything is working fine, BUT if i modify a template file (header-extensions.php) located in the PARENT theme directory, i can’t seem to connect to the database.

code that works fine in a php file located in my CHILD theme folder works, such as

global $wpdb;
$lightboxes = $wpdb->get_results( "SELECT * FROM wp_usermeta WHERE meta_key = 'lightbox' AND user_id = $user_ID");
<select>
<option>--Select from your lightboxes--</option>
    <?php

	foreach ($lightboxes as $lightbox) {
		if ($lightbox->meta_value != $editLB) {
			echo '<option>'.$lightbox->meta_value.'</option>';
		}
	}

	?></select>

but, the following code, while it seems to connect to the database, returns no results

<?php
						global $wpdb;

						if ($user_ID) {
							$getLightboxes = $wpdb->get_results( "SELECT * FROM wp_usermeta WHERE meta_key = 'lightbox' AND user_id = $user_ID");
						}

						if (!$getLightboxes) {
							echo '<li><a href="https://therapytest.com/wordpress/?page_id=40">You have no lightboxes</a></li>';

						} else {
							foreach ($getLightboxes as $lightbox) {
								echo '<li><a href="">'.$lightbox->meta_value.'</a>
								<ul><li><a href="">view</a></li></ul>
								</li>';
							}
						}
						 ?>

is there any reason why i am unable to connect to the database and/or return results from the files located in a PARENT theme folder?