RSS Feeds Now Validating

Someone dropped me a line earlier this evening to say that my RSS and Atom feeds weren't validating correctly. I'm not sure if this is following my site upgrade or if they ever validated before, it looks like from this article Moveable Type has a history of generating invalid RSS feeds. Luckily the same article has feed templates that do validate, so I did a quick template replace on my site and it looks like they validate now. Here's the updated set of URLs for my feeds:

• RSS1.0 : http://www.rittman.net/index.rdf - according to this feed validator, "This feed is valid, but may cause problems for some users" . It works fine in Thunderbird though.
• RSS2.0 : http://www.rittman.net/index.xml - according to the same validator, "This is a valid RSS feed."

No joy with the Atom feed though - I tried the one at this site but it still comes across as invalid. If anyone knows more about Atom (and ideally, Moveable Type 3.2) and can tell me what's wrong, I'd be grateful. I'll update the pages on the site soon to reflect the feeds that validate OK.