I created a custom post type for Products.  I can display all the fields no problem (either in a list or a single-product.php).  I wanted to use the Media library and associate an uploaded picture with the Product post type (mostly to handle all the thumbnail work automatically). I uploaded a photo to the media library and associated with a specific Product post type.

     $args = array(
    		'label' => __('Products'),
    		'labels' => $labels,
    		'public' => true,
    		'can_export' => true,
    		'show_ui' => true,
    		'_builtin' => false,
    		'capability_type' => 'post',
    		'menu_icon' => get_bloginfo('template_url').'/functions/images/product.png',
    		'hierarchical' => false,
    		'rewrite' => array( "slug" => "product" ),
    		'supports' => array('title', 'thumbnail'), //MAYBE add thumbnail later!
    		'show_in_nav_menus' => true
    		
    		);

I've tried everything to display the thumbnail and picture for the Product but it's not working:  `the_post_thumbnail();`, `get_the_post_thumbnail`  but nothing works.  Here's my single-product.php:

          <div class="post_content">
			<?php 
				$attachment_args = array(
					'post_type' => 'attachment',
					'numberposts' => -1,
					'post_status' => null,
					'post_parent' => $post->ID
						);
						
				$attachment = get_posts($attachment_args); ?>
			<img src="<?php echo wp_get_attachment_image_src($attachment->ID, 'full', false); ?>"  />
			
			
			<p><?php echo get_post_meta($post->ID, $prefix.'description', true); ?></p>
			<ul>
			<?php //this gets the custom fields for the document links (PDF Files)
			  $custom_field_keys = get_post_custom_keys();
			  foreach ( $custom_field_keys as $key => $value ) {
			  	$valuet = trim($value);
			      if ( '_' == $valuet{0} || $prefix != substr($valuet, 0, 4) || $prefix.'description' == $valuet )
			      continue;
			    $n = substr($valuet, -1);
			    
			    if ( $valuet == $prefix.'docname'.$n)
		     		echo '<li><a href="' . get_post_meta($post->ID, $prefix.'docurl'.$n, true) . '" target="_blank">' . get_post_meta($post->ID, $prefix.'docname'.$n, true) . '</a></li>';	    
			  }
			?>
			</ul>
		</div><!-- end post_content -->

Am I missing something?  Thank you!