i was using an old version of arras with a custom field of thumbs to display post thumbnails.
In the process of upgrading templates and with 6600 posts I dont want to change this by hand - so i changed field thumbs in wp_postmeta table to _thumbnail_id but the images are still not displaying.
If look into individual post db records - a post that has the thumb selected manually from nextgen gallery has the following format
whereas my "older" fields show as
and doesnt display