"Failed to find messages" usually means that default selectors aren't good. They work fine for 90% of the sites, but some sites have custom styling templates.
For that reason (to support all sites) custom selectors where added.
You most likely just need to add custom selectors as described:
http://leecher.freddy.lt/faq.php?expand=faq206I could only take a look knowing the URL.
Also, maybe the forum doesn't show content (topics) if not logged in. You will then need to save account in "WEBSITES" -> select that forum -> "User" tab (only if really needed, otherwise it will just decrease performance).