Plugin stopped working

Since I upgraded to 2.9, a plugin I wrote (for internal use) stopped working. I’ve been trying to look at any parameters which might have changed names, but couldn’t resolve any possibility. Can anyone have a quick look, and tell why it doesn’t work? I tried outputting statements to log-files in several parts, but plugin doesn’t even seem to be called…

function shorten_url() {

	global $post_ID, $wpdb, $table_name;

	$table_name = 'wp_5c4ujq_shorturl';

	$post = get_post($post_ID);

	if (get_post_meta($post_ID, "short_url") != "") {
		return true;
	}

	$max_short = $wpdb->get_var("SELECT short FROM $table_name WHERE id = (SELECT MAX(id) FROM $table_name)");
	$new_short = alphaincr($max_short);

	add_post_meta($post_ID, "short_url", "http://nwt.rs/" . $new_short, true);

	$link  = get_permalink($post_ID);
	$title = $post->post_title;
	$content = $post->post_excerpt;
	$stamp = date();

	$wpdb->insert($table_name, array('short' => $new_short, 'url' => $link , 'title' => $title), array('%s','%s','%s'));

	$length = strlen('http://nwt.rs/' . $new_short) + strlen('Nieuw artikel: ');

	if (strcmp($title, substr($title, 0, 140 - $length)) == 0) {
		$twitter_title = $title;
	} else {
		$twitter_title = substr($title, 0, 140 - $length - 3) . '...';
	}

	to_twitter('Nieuw artikel: ' . $twitter_title . ' - http://nwt.rs/' . $new_short);
	to_facebook($title, 'http://nwt.rs/' . $new_short, $content);

}

add_action('publish_post', 'shorten_url');

The other functions that are called, have nothing to do with WP, and should work fine. I know code isn’t all that clean, but this is for internal use only.

All help is more than welcome !