Podcast Submit Error 504

This page explains what a 504 error is: http://www.checkupdown.com/status/E504.html

Your feed URL, http://www.rajahrabbit.com/feed/podcast/shoubaodate , works when subscribing manually in iTunes. In Firefox (my default RSS reader) the first time I accessed it it showed a web page, though subsequently it showed the feed as I would have expected. The actual feed coding seems to be pretty well OK (FeedValidator throws up a few minor points, see their report).

I can only guess at what is going on, but possibly your server is set up to feed a different result depending on what sort of client makes the request, so that an RSS reader gets the feed but a browser sees a different version (though I couldn't subsequently reproduce what happened the first time). In this even some sort of detection system is running and the iTunes Store may be upsetting it.

I can't advise on Wordpress and I know nothing at all about the plugin you mention. It seems possible that the issue lies with the server you are using rather than the plugin, so you should make sure that it simply serves up the feed in the way a simple webspace server would do, without trying any clever redirects (as is suggested by the 504 error).