Thumbnail now showing? No idea whats wrong :(

This is the code I have

” title=”<?php the_title(); ?>”>
<img src=”<?php $values = get_post_custom_values(“thumbnail”); echo $values[0]; ?>” alt=”<?php the_title(); ?>” class=”thumb” />

<?php the_excerpt(); ?>

im adding key field of “thumbnail” (no quote marks) and a direct link to the image. Any idea whats wrong?