This article may help: http://rfwilmut.net/notes/diagnose.html
and see also https://help.apple.com/itc/podcasts_connect/#/itc561d27981
The checking procedure I use with a query like yours is first to go to the iTunes Store page (hopefully the questioned provides a link, though usually the title will enable finding it) and see what is listed there. Then I subscribe from the button on the Store page. I go to the Podcasts section and see what's listed there. I then control-click (Mac - right-click on Windows) on the title of the Podcast (not on an episode) and choose 'Copy Podcast URL' to get the feed URL; I compare this with the URL given by the poster - sometimes it's not the same and they have been updating the wrong feed. Indeed the URL you give for your feed in your first post is correct but the actual URL in the link is not.
Common errors which can completely wreck a feed are using an ampersand by itself, or forbidden characters such as control codes, 'curly quotes' or other strange characters.
Only certain media file types are allowed - .mp3, .m4a, .m4v, .mov or .mp4 file (not Windows Media, RealMedia, YouTube or Flash). If the 'type' attribute inside the 'enclosure' tag doesn't match the format of the actual file the process will fall over as iTunes tries to use the wrong codec. Also the media file filenames must not have spaces in them - spaces are not allowed in a URL and although browsers and some readers will correctly substitute the code %20 for each space, iTunes and Podcasts Connect do not and so see the URL ending at the first space.
Although you've had a lot of experience with podcasting, you might find some parts of my 'Get you started' page helpful - http://wilmut.uk/pc
If all else fails... post here!
