I'm not sure. The last 4 episodes have a
<itunes:duration> value greater than 1 second. The older episodes have the value 0:00:01.
One thing which could be the source of the problem is that the file names of the media files contain white spaces. That is okay on a personal computer. But internet servers or scripts on servers could have problems with these file name.
I recommend that you use underscore or hyphen characters instead of the white spaces.
Another reason why a player does not play media files is some times because of the format/type of the files. Maybe you could re-encode the file with a different audio software. But this situation is more unlikely. That is why you should try the other idea first.