<pubDate>Jan 18 2006 04:36:40 -0500</pubDate>
isnt a RFC 822 date.
to create one with php you could use
strftime('%a, %d %b %Y %H:%M:%S -0500',time());
basicly to make your pubdate work you need to swap the date (18) to before the month
<pubDate>Wed, 18 Jan 2006 04:36:40 -0500</pubDate>
should work.
read the rfc next time
http://www.faqs.org/rfcs/rfc822.html