RSS Weirdness

The configuration of my site is admittedly very strange. It is comprised of multiple WP installations, each with their own database. Each uses the exact same theme. It is all linked together via the menu for a seamless appearance to my visitors. To display information from one installation to another, I use RSS. The site consists of a main section (contains the homepage and about us info); a beverages section; a blog section; a section with food information; a recipes section; a glossary section; and a magazine section. On the homepage, the latest content from each of these is displayed via RSS, changing daily.

All the WP installations and plugins are up to date.

Suddenly, several of the RSS feeds stopped showing. They don’t display no matter what method is used to call them, nor what browser is used to view the site. The homepage displays “Error: Feed has a error or is not valid” but in other places, using a different plugin or WP component, there’s no message at all. To see this variable, check the homepage at http://www.epicurus.com and the bottom of http://www.epicurus.com/advertise. Errors also show up in the sidebars (using the default WP RSS widget) at http://www.epicurus.com/magazine. On that same page, you’ll see that the feeds fail to display in some of the boxes, but using a totally different RSS plugin than the homepage.

You’ll see that the feeds from /beverages; /food; and /Glossary do not show, however, in running the WC3 Feed Validator, each tests perfectly.

I’ve tried the standard deactivation of all plugins, which didn’t change anything. I have even tried reinstalling WordPress in one installation.

So, my questions are:
1. Has anyone seen this kind of unusual behavior before?
2. Does anyone know how to identify the cause or affect a solution?

Thanks in advance.