The file names cannot be more than 50 characters (including .mp3), otherwise the podcast uploaded cuts off the file name, which is while the files will not play.
Eliminate any non-letter characters (.:,- etc) from file names to ease the upload and post process. (Can still be in the title when posted.)
80 kbps is appropriate quality for spoken word. Music would require 128 kbps. The files need to be less than 40MB as well.
The author field has to be a limited number of characters.
All fields have to be filled out.