Spent an hour seeking a solution for my inability to burn a Feedburner feed. Feedburner could not find the feed page on my site - when I tried to burn a feed, it returned a "page not found" error.
The solution turned out to be very simple. I had deleted all posts on the site and created the site using pages. In order for Feedburner to burn a feed, there must be at least one post on the site!
So, do try this first, before you try the often very complex suggestions offered for this problem. Hope this saves you some hair loss.