Many years ago Feedburner was a useful service. It proxied the RSS feed of your blog and gave you analytics of what happened with it. Now feeds using Feedburner randomly give HTTP error 404s. The Feedburner Twitter account is inactive and recommends that people Tweet at Google instead. It seems that Google wants to get rid of the service and random 404s probably aren’t a high priority for them.
I’ve just gone through the config for Planet Linux Australia and changed as many Feedburner URLs as possible to direct feed URLs. I did this by loading the Feedburner feed, getting the URL for the site, and then guessing the feed URL (usually just appending “/feed” to the domain name).
I recommend that everyone abandon Feedburner, it’s not reliable enough to use and doesn’t seem to have any active support.