Cannot get post thumbnails to display

I’m stumped. I’ve pored over all the articles here and beyond to no avail. I’m trying to simply display the post thumbnail in a template page, but it will not show up.

I have thumbnails enabled for the theme in functions.php: add_theme_support ('post-thumbnails');

I removed the sizing function set_post_thumbnail_size( 150, 150 ); from functions.php and added array(150,150) as an argument to get_the_post_thumbnail

I’ve set the Featured Image in a couple posts to test it out.

I tried echoing out get_the_post_thumbnail and using the_post_thumbnail template tag. I tried both get_posts (along with setup_postdata($post);) and new WP_query methods. No such luck.

I don’t think it matters, but I’m using a child of the Twenty Eleven theme.

I have a template page set up and I’m calling a function I created in functions.php to list the posts. I’d like to use get_posts and echo it out like this: get_the_post_thumbnail( $post->ID, array(150,150) ). I’ve also tried inserting the function straight into the template page.

I’ve made every tweak I could think of. I don’t see anything I’m overlooking, seems pretty straight forward. Any ideas? Any help would be greatly appreciated.

Here’s the code I had initially before trying all the tweaks mentioned above.

In the functions.php file:

if ( function_exists( 'add_theme_support' ) ) { 
add_theme_support( 'post-thumbnails' ); 
}

set_post_thumbnail_size( 150, 150 );

And in my page template file:

function list_posts_by_cat_auth_year ($cat_text, $cat_id, $author, $year) {

echo '
<h1>'.$cat_text.'</h1>
<br />
<ol>';
global $post;

$args = array( 'posts_per_page' => -1, 'numberposts' => 0, 'category' => $cat_id, 'author' => $author, 'order' => 'desc' );

$myposts = get_posts( $args );
    foreach( $myposts as $post ) {
        $author = get_userdata($post->post_author);
        echo '
        <li>
        <div style="float:left">'
        .get_the_post_thumbnail( $post->ID, array(150,150) ).'
        </div>
        <a href="'.get_permalink().'">'.get_the_title().'</a>
        <br />
        <span class="post-summary">Posted on '.get_the_time('D, M jS, Y').' by '.$author->first_name.
        '<br />'.
        get_the_tag_list('Tagged:  ',' , ','').'
        </span>
        <br />
        ';

        echo '
        </li>
        <br />';
    };
echo '
</ol>
';
}