Custom field code — what is wrong with this?

I have a piece of code that isn’t working and I can’t figure out what is wrong with it. (some of my code is being truncated, by the forum, but hopefully the important stuff is showing up)….

<?php foreach($results as $cat){ ?>
<h3 ><a href="<?php echo get_category_link($cat->cat_ID); ?>">
<?php echo $cat->cat_name; ?></a></h3>

    <select name="category" style="font-family: arial,verdana, sans-serif;font-size:9pt" onchange="MM_jumpMenu('parent',this,0)">
    <option value="">Sermon Series on <?php echo $cat->cat_name; ?></option>
<?php query_posts('category_name='. $cat->cat_name . '&showposts=-1&order=ASC'); ?>
<?php while (have_posts()) : the_post(); ?>
<option value="<?php the_permalink(); ?>">
<?php the_title(); ?>
<?php get_post_custom_values('Subtitle'); ?>
</option>
<?php endwhile; ?>
</select>

This works for the most part, displaying a drop-down list of posts in the category. I am trying to add a custom field value, so that the list shows titles AND subtitles. But the code for subtitle is not working, and I can’t see the mistake.

<?php get_post_custom_values('Subtitle'); ?>

This works elsewhere just fine, but in this drop down list, I only get the word “Array” in it’s place. I hope someone who hasn’t grown code-blind over this can help me. I am probably missing something obvious.

Thanks in advance. ??