I just spent the last few hours trying to figure out why my global posts feed broke all of a sudden.
Turns out, if an ampersand is added to a post title without entering it as a character entity, the feed breaks. This happens in Chrome and IE9. The page renders in Firefox. It makes no difference who adds the ampersand throughout the network. If anyone does - the entire recent global posts feed goes down.
The message I get in Chrome is as follows
error on line 18 at column 19: xmlParseEntityRef: no name
The line and the column referenced are where the ampersand is causing problems. Removing the ampersand from the post title, or changing it to an entity fixes the feed.
Normal feeds and the recent posts plugin are unaffected.
I tried disabling all plugins and it didn't make any difference so this doesn't appear to be a conflict.
I'm using the latest versions of everything on a multi-site setup.
Maybe someone else could try this and see if you are getting these results(?) This would seem to be a problem with the plugin itself.