Another silly thing. I found the error occurred even less with the super cache. Makes no sense to me but I thought people would like to know.
Silly thing but I found mines to work once i enabled the WP-Cache or the WP-Supercache. Totally unrelated and irrational but worked for me.
I found I had the same problem last night. I agree it might be the new WP version. However I also noticed that if you turn on WP-Cache and you go to your RSS link you get XML output but without the standard feed format. After refreshing, it fixes itself. The two things are totally unrelated but somehow work (?). It really confuses me but at least gets your feeds kinda working. Anyone have any idea why this is?