Podcast URL is not valid anymore

As you haven't posted the URL of the feed file I can only get this from iTunes, which I can't access at the moment (being on Linux): I will try to do so tomorrow morning, but if you read this before I do it would be helpful if you could post the URL (please include the http://).

Your feed is missing the declaration at the top, without which iTunes cannot read any of the 'itunes' tags. The top section of your feed should look like this:

<?xml version="1.0" encoding="UTF-8"?>
<rss xmlns:itunes="http://www.itunes.com/dtds/podcast-1.0.dtd" version="2.0">
<channel> - and so on

Also, 'keywords' is not a recognized tag (though it will just be ignored); and 'author' should be 'itunes:author'.

Your feed is missing a number of tags, which probably won't prevent it working, but it would be better to use them. This page gives you a basic feed:

http://www.wilmut.org.uk/pc

You have an unclosed tag; line 14 reads

<itunes:name>B-K Lighting, Inc.<itunes:name>

it should read

<itunes:name>B-K Lighting, Inc.</itunes:name>

This renders the feed unreadable but correcting it should make it work OK: you can test it by subscribing manually from the 'Advanced' menu in iTunes.

It normally takes 1-2 days, but sometimes several days.