WordPress 404 error on comment submission
For more than six months whenever a visitor submitted a comment on this blog, he would be greeted with a 404 error. I blamed this on the advanced permalinks migration plugin and never got around to fixing it. It turns out that this may not be a fault of that plugin after all. It’s something else that’s broken; paginated comments (or at least this is the impression I got from reading several posts on different blogs on the topic).
The solution it turns out is trivial (I am kicking myself for not fixing this earlier). I found it on http://wordpress.org/support/topic/254939; all you need to do is to turn off paginated comments!