I got a wp theme that can display a category page with thumbs (of posts)

        $cat_args = array(
          'orderby' => 'name',
          'order' => 'ASC',
       // 'number' => $num,
          'child_of' => 0,
          'show_count' => 1
          );
     $categories =   get_categories($cat_args); 
     foreach($categories as $category) {
    echo '<a href="' . get_category_link( $category->term_id ) . '" title="' . sprintf( __( "Toutes les vidéos de %s" ), $category->name ) . '" ' . '><div class="video video_">';
    echo '<h3>' . $category->name.'</h3>';
	
	
     $post_args = array(
      'numberposts' => 1,
      'category' => $category->term_id 
    );
    $posts = get_posts($post_args);
	foreach($posts as $post) {
	?>
		<div class="thumbnail">
			<?php if ( has_post_thumbnail() ) { echo the_post_thumbnail();}else{ ?>
				<img src="<?php echo get_post_meta($post->ID,   get_option('wptuber_thumbs'), true); ?>" alt="<?php the_title(); ?>" />
			<?php } ?>
		    </div>
		<?php 
		} 
	echo '<em>Toutes les videos ('.$category->count.')</em>';
	echo '</div></a>';
    } 
    ?>


but when I try to change it to get the same with "tag" every thing works fine but the thumb is not showing. Can someone help me?

        $tag_args = array(
        'orderby' => 'name',
        'order' => 'ASC',
     // 'number' => $num,
        'child_of' => 0,
        'show_count' => 1
         );
    $tags =   get_tags($tag_args); 
    foreach($tags as $tag) {
       echo '<a href="' . get_tag_link( $tag->term_id ) . '" title="' . sprintf( __( "Toutes les videos de %s" ), $tag->name ) . '" ' . '><div class="video video_">';
    echo '<h3>' . $tag->name.'</h3>';
	
	
    $post_args = array(
      'numberposts' => 1,
      'tag' => $tag->term_id 
    );
    $posts = get_posts($post_args);
    foreach($posts as $post) {
    ?>
    	<div class="thumbnail">
    		<?php if ( has_post_thumbnail() ) { echo the_post_thumbnail();}else{ ?>
    			<img src="<?php echo get_post_thumbnail($post->ID, get_option('wptuber_thumbs'), true); ?>" alt="<?php the_title(); ?>" />
    		<?php } ?>
    	    </div>
    	<?php 
    	}
    
    	echo '<em>Toutes les videos de ('.$tag->count.')</em>';
	echo '</div></a>';
    } 
    

What am I missing?