Use Auto-Generate-Thumbnail plugin to generate thumbnail images when has_post_thumbnail is erroring out. This assumes you are inside of the WordPress loop.

has_post_thumbnail_fail.php

<?php
//Assumes within the WordPress Loop 
$args = array ('title'	=> $post->post_title);
if ( strlen( $img = get_the_post_thumbnail( get_the_ID() ) ) ) {
	/* display thumbnail */
	the_post_thumbnail( 'thumbnail', $args );
} else {
	delete_post_meta( $post->ID, '_thumbnail_id' );
	//Requires Auto Post Thumbnails plugin - http://wordpress.org/extend/plugins/auto-post-thumbnail/
	if ( function_exists( 'apt_publish_post' ) ) {
		apt_publish_post( $post->ID );
	}
	the_post_thumbnail( 'thumbnail', $args );
}
?>