Hey,
I'm having the same issue.
Here's my feed link:
http://www.12steprecovery.com/index2.php?option=com_podcast&feed=RSS2.0&no_html=1
I'm getting the 500 error when I submit to iTunes.
Here is the strange thing, it was working for a long time, then they dropped it this week for the 500 error. However, following their advice, I can manually subscribe in iTunes and download every episode and listen to them.
Only thing that may be considered different is that I'm offloading the .mp3s to Amazon S3 and using that url to serve up the podcasts. It still works manually though.
Any ideas folks? Thanks in advance.
Jonathan