I've had this problem in the past, but I've always found a culprit. I thought I recalled finding a solution in the forums in the past, but I can't today.
My feed (http://o2b.net/feed/) has an unclosed CDATA section. I know it has to do with the most recent post, but I've picked it apart for an hour, I can't find what specifically is causing the problem.
This happens on a frustratingly regular basis.