I just had some troubles for a few days trying to figure out why some of my feed were disappearing from Magpie when the website was using feedburner’s services ; the problem was coming from user agent - feedburners apparently has some troubles answering application with a ‘weird’ name.
The solution I found (here) is to declare Magpie useragent as being something more traditionnal:
define('MAGPIE_USER_AGENT', 'Mozilla/5.0 (Windows; U; Windows NT 5.1;
en-US; rv:1.9.0.1) Gecko/2008070208 Firefox/3.0.1');
* Magpie is a RSS parser for PHP; it allows for quick prototyping. It is super simple and easy to use. It is a very nice way for using similar concepts as the Yahoo Pipes RSS parser in custom code.