thanks for that advice - it's solved that error message but unfortunately it doesn't return any posts.

I've found there are 2 LatestPost functions, one in Forum.php and one in Post.php (both in forum/code).

Post.php:
   function LatestPost() {
      $filter = "";
      if($this->ParentID != 0) {
         $parents = $this->getDescendantIDList();
         $parents[] = $this->ID;
         $filter = "AND ParentID IN (" . implode(",", $parents) . ")";
      }
      $posts = DataObject::get("Post", "TopicID = $this->TopicID $filter",
                                           "Created DESC", "", 1);
      if($posts) return $posts->First();
   }

Forum.php
   /**
    * Get the latest posting of the forum
    *
    * @return Post Returns the latest posting or nothing on no posts.
    * @todo This is causing some errors, temporarily added is_numeric.
    */
   function LatestPost() {
      if(is_numeric($this->ID)) {
         $posts = DataObject::get("Post", "ForumID = $this->ID",
                                              "Created DESC", "", 1);
         if($posts)
            return $posts->First();
      }
   }

As you can see, they are similar but different.

And now I have 2 LatestPosts functions, one also in Forum.php and one in mysite/code/page.php as per the code posted in previous messages

So it compiles and runs, but doesn't actually produce any code in the resulting html. HELP!