RSS feed will not validate- Error 404: Not Found

Though my blog pulls up in my browser fine, it is not validating through feedburner or validator.w3.org. This is the message I get: http://validator.w3.org/feed/check.cgi?url=http%3A%2F%2Fdavidjameskeaton.com%2Fspiderblog-3%2Ffeed

From what I’ve read on these forums, I imagine it has something to do with script that the validator won’t accept (from composing posts in Word, which we will not be doing anymore), but I don’t know how to identify the existing code problem and fix it.

The blog is at http://davidjameskeaton.com/spiderblog-3/

Any thoughts? Thanks for your help!