I've heard from several people that ordinary use of the comments has been triggering the Bad Behavior plugin, usually with an error that the "user agent has changed since the page was downloaded." The only thing that has changed recently has been turning on the WP-Cache plugin for the whole site. I've upgraded the cache and Bad Behavior plugins. If you are reading this, could you just please try to leave me a test comment on this post and email me if you have problems. Thanks.