Although the iTunes Store is showing episodes up to March 30, your feed does not work when subscribing and also comes up empty when accessed in FireFox. This means that you have introduced a fatal error which is rendering it unreadable.
FeedValidator flags the 'link' tag in your top episode:
<link>http://www.CalvaryNewberg.org/index.php?option=com_biblestudy&view=sermon&id=903 &t=1</link>
presumably because of the ampersands ('&'). You can't have an ampersand by itself in XML because it signifies the beginning of a code sequence which is then never completed, thus wrecking the rest of the feed.
Its presence here is part of PHP coding, so I dont' know whether this is what's wrecking things - I can't see anything else dubious. You have the same link in every episode (or something similar). Has the feed ever worked when subscribing? or have you added these link tags recently? I wonder whether the Store (which is different programming from the iTunes application) isn't thrown by this but other areas are.
Anyway, your first move would be to remove them from every episode (they aren't doing any good within an episode tag anyway so you might as well remove them).
Then re-upload the feed and subscribe in iTunes from the 'Subscribe' button on your Store page and see whether the episodes now show.