I have encountered the same issue. I was on 2.6.3 version and moved my feedburner feed to feedproxy.google.com with 2.6.3 and it was working fine.
However now I have upgraded to version 2.7 and the feed stopped working. When I click to subscribe I get an error message that states:
Bang! Kapowww! Krakkk!
(FeedBurner encountered an error while trying to bring you this feed and is now keeping its head down. Details follow.)
Feed Address: https://feedproxy.google.com/vikitech
HTTP Error Code: 502
Detail: There was a problem retrieving the feed: Error getting URL: 404 – Not Found
My comments feed is working fine.
When I ran the feed through the validator I am getting a message that says:
Server returned HTTP Error 502: There was a problem retrieving the feed: Error getting URL: 404 – Not Found
I am using the feedburner feedsmith plugin and tried deactivating that, but It didnt work.
I have searched on the net regarding the same issue and I see a lot of guys are facing the same issue, not many have posted here though.
Can someone please help me out? Its a real difficult situation if a blog doesnt have a working RSS feed…Any suggestions please?