[BirdOPrey5]

This exact code works for me...

include('includes/functions_forumlist.php'); 
global $vbulletin, $lastpostarray;

// call fetch_last_post_array() first to get last post info for forums
cache_ordered_forums(1);
if (!is_array($lastpostarray))
{
	fetch_last_post_array(-1);
}

   $forumidx = 1;  //Set your forum id to check here

   $lastpostinfo = (empty($lastpostarray[$forumidx]) ? array() : $vbulletin->forumcache["$lastpostarray[$forumidx]"]);
   $forumx = $vbulletin->forumcache["$forumidx"];

   $isnew = fetch_forum_lightbulb($forumidx, $lastpostinfo, $forumx);

   if ($isnew == "new")
  {
          //Execute code here if the forumid chosen above contains new posts

     $newmsg = "Yes";   

  } else { 

    $newmsg = "No";         



  }

In your vBulletin Options -> General Settings -> Thread/Forum Read Marking Type, is it set to Database (automatic forum marking)? It may need to be for this to work.