FeedValidator is one of the most popular online utilities for validating RSS and Atom feeds. Not only does it tell you if there are any errors in your feed but it also suggests how to ensure that your feed is compatible with the widest range of feed readers. It’s quite useful both for bloggers and developers … Enter the address of your feed or blog and see if your RSS feed is working/valid.
If you are a developer you might also find useful their recommendations for how to create RSS 2.0 documents that works with all software that supports this format.
Check out FeedValidator @ www.feedvalidator.org