The <tumb> tag generated for TV Episodes (the top level folder) is bogus (at least in the version I have).
Here is an example:
<thumb><thumbs><thumb>http://thetvdb.com/banners/posters/79488-4.jpg</thumb><thumb>http://thetvdb.com/banners/posters/79488-1.jpg</thumb><thumb>http://thetvdb.com/banners/posters/79488-3.jpg</thumb><thumb>http://thetvdb.com/banners/posters/79488-2.jpg</thumb><thumb>http://thetvdb.com/banners/graphical/79488-g.jpg</thumb><thumb>http://thetvdb.com/banners/graphical/79488-g5.jpg</thumb><thumb>http://thetvdb.com/banners/graphical/79488-g4.jpg</thumb><thumb>http://thetvdb.com/banners/graphical/79488-g6.jpg</thumb><thumb>http://thetvdb.com/banners/text/79488.jpg</thumb><thumb>http://thetvdb.com/banners/graphical/79488-g3.jpg</thumb><thumb>http://thetvdb.com/banners/graphical/79488-g2.jpg</thumb><thumb type="season" season="1">http://thetvdb.com/banners/seasons/79488-1-2.jpg</thumb><thumb type="season" season="2">http://thetvdb.com/banners/seasons/79488-2-2.jpg</thumb><thumb type="season" season="3">http://thetvdb.com/banners/seasons/79488-3.jpg</thumb></thumbs></thumb>
Quite frankly, I have no idea what goes in there (asked in the XBMC forums but no answer, yet) but this certainly isn't right. It looks like the tag has tags inside it converted to entities (> <, etc.)
I apologize if this is already addressed.