Using WP 3.5.1
Smart Manager Lite 3.1.2
When in the post edit screen, when I click the 'Set Featured Image' link I get the popup. The first thumb in the pop-up is blank - viewing the HTML in Chrome inspector reveals that there is no image tag for the thumb.
While in the pop-up if I select the desired thumbnail and click the 'Set featured image' button, the pop-up goes away, but the featured image does not get set.
If I deactivate 'Smart Manager Lite', I have no issues setting the featured image.