It needs an update because themoviedb.org changed it’s API which caused Thumbgen to not work correctly for moviesheets. There are many many posts on this board about this.
Here is one of them, you can read all about it.
There is a nice tutorial created by Tinwarble on how to use Thumbgen for TV shows. You can find it here. I suggest you download it and read it. It will show you what settings you need.
