Figured it out!
It was the bbPress Sitemaps plugin!
http://premium.wpmudev.org/project/bbpress-sitemaps
It hasn’t been updated lately and that was the issue. Thank goodness it was something easy! I was reading it as a BuddyPress plugin, which is why I didn’t disable it first. Doh!
Wow — I love you!! Thank you so much for doing this! (What screencast software are you using? It’s fabulous!)
