Can't get post thumbnail to show

[albertocv]

I'm trying to write a custom homepage for my wordpress blog.
I want to show the top 5 posts from three main categories on columns and I managed to do it.
Next to each post link I want to include the post thumbnail but I can't get it to show. This is the code I'm using:

<?php
 					$posts = get_posts('numberposts=5&category=86');
 					foreach($posts as $post) :
    				setup_postdata($post);
					if ( has_post_thumbnail($post->ID) ) { 
						echo get_the_post_thumbnail( $post->ID,array(100,100));
						}	
				?>
				<p>
				<a id="post-<?php the_ID(); ?>" href="<?php the_permalink(); ?>">
				<?php the_title(); ?></a></p>
				<?php endforeach; ?></div>

I verified that each post has a thumbnail and that thumbnails are supported by the theme. However nothing is output by the call to get_the_post_thumbnail.

What am I doing wrong?