Some people use the "Post Feed Redirect" setting improperly. When this is done, the problems created can be easily solved, by clearing the setting.
- Go to the dashboard menu Settings - Other - Site feed.
- Look at the entry for "Post Feed Redirect URL".
- If that option is incorrectly set, click on "Remove".
- Click on "Save settings".
- You're done.
If you actually need the feed redirected, it's similarly simple to set it.
- Go to the dashboard menu Settings - Other - Site feed.
- Look at the entry for "Post Feed Redirect URL".
- If that option needs to be set, click on "Add".
- Paste or type the correct URL, into the box.
- Click on "Save settings".
- You're done.
The setting, for this blog, for instance, is:
http://feeds.feedburner.com/FixTemplates-Blogging
The dashboard Settings - Other page.
The Post Feed Redirect URL setting, in the "Site feed" section of Settings - Other.
Just understand what the setting does, how to clear, and how to add, the setting - and when you should use it, or not use it.
If FeedBurner is involved, check out an example connecting FeedBurner using the Post Feed Redirect.

