I was adding Feedburner to my site today. I had use it once, switched templates and put off editing the template. Then I realized my feed had an error in it. For how long, I didn't know. I deactivated the Feedburner plugin and still had an error. I made the last post private, just in case it had a weird character in it somewhere, because the feed ended abruptly with the first post body. That didn't fix it. I have a lot of plugins now, so I didn't want to go through deactivating all the plugins and checking the feed after activating each one.
Instead I did deactivate all of them to see if this fixed the issue which it did. Then I downloaded the errorlog file from my server. I found the same error, over and over again:
Call to undefined function get_caption() in /wp-content/plugins/sem-extract-terms/sem-terms2posts4feeds.php on line 181
So, I searched for "Call to undefined function get_caption()" on Google, which gave me a lot of other feeds with the same issue, but no info. But the error was in the Related Entries for Feeds plugin, which I no longer needed since I was using Feedburner. So I reactivated all plugins except it. Just something to watch for and help for anyone else who may be searching for this issue on Google and not finding it.