Found a bit of an unusual one today when checking out a new site in Google Webmaster Tools.
GWT was reporting that there was a huge number of links pointing to mywebsiteurl.com/comments/feed/ and that the feed’s URL was 404 not found.
Turns out that the site itself hasn’t had any comments yet so while the RSS feed URL was still being generated it was 404 because the feed itself didn’t have any data to draw on.
I guess the same would happen with the Posts Feed as well if you didn’t have any posts (haven’t checked).
Pretty simple really, the solution was to make a comment.
I have a particular category that doesn’t show the comments, but you could simply make a fake comment as a logged out user or hide the comments on an individual post and just make a random comment as yourself.
Once the comment is in the system the feed URL magically works again and it generates the RSS feed.
WordPress is a crazy little beast sometimes….