RSS feed from site invalid to several browsers and feedburner

Hi, I have dealt with this in the past, and I think the core updates of WP solved it at one point. I cannot get an rss feed out of my sites. generates errors. Many others are having the issue, too, I see in my google searches. The usual fix rss plugin does nothing to solve it.

I have seen some elaborate edits of the WP core files, and I tested a couple of a test site.

Does anyone know an easy fix? (Okay, even a difficult fix would be appreciated!)

Here is a sample site I am testing:

The error is that in chrome, firefox, safari it attempts a "download." Works on a windows explorer. Feedburner errors on it, and several others that I have recently updated in WP to 3.4.2. (Yes, there are posts that could be displayed in the RSS.)

I saw this:
Does anyone trust doing that? On another test site it took away the error but gave me an empty feed.

Please advise.