Can manually subscribe in iTunes but not submit to store

As far as I can see your feed is OK, with one possible exception. The declaration at the top reads:
<rss xmlns:feedburner="http://rssnamespace.org/feedburner/ext/1.0" version="2.0">

This may contain the necessary information (as you can subscribe manually it may well do so) but normally you would include the itunes declaration so that it would read:

<rss xmlns:feedburner="http://rssnamespace.org/feedburner/ext/1.0" version="2.0"
xmlns:itunes="http://www.itunes.com/dtds/podcast-1.0.dtd" version="2.0">

In any case, someone else is complaining of the same thing; I can only guess that there is a problem at the Store end. We've seen this before, with people finding they can't submit for some days. There probably isn't really anything you can do except just keep trying.

Again, this feed appears to be fine (and might be the preferable one to submit to iTunes as it's less cluttered and does have the correct declaration). Though obviously I can't say for sure, I would think it's a problem at the Store end and there isn't really anything you can do about it except to try from time to time.

Glad you got it sorted.