Sorry if I’ve not made myself clear, but when you click the ‘Post Status’ button, you are automatically taken to a page called http://www.example.com/activity/post – which doesn’t exist. Just tried a few other BP sites and when you leave a status update on those you stay on your profile and the status appears, but now on mine you are re-directed, but because the page doesn’t exist, the status doesn’t post.
There is an activity page and a place to post a status, but when you click ‘Post Status’, it takes you to http://example.com/activity/post – which doesn’t exist so displays a Page not Found. The http://example.com/activity page does exist and is functional.