WordPress help

I’m getting an error on some — but not all — pages, a 412 error: “Precondition Failed. The precondition on the request for the URL /wp-comments-post.php evaluated to false.”
If you try to post a comment on the post below, for example, I get the error.
In the support forums, I see something about Bad Behavior, a spam filter, but I use Spam Karma. I deactivated and activated it; no difference.
I also got this error just going from one page in an archive to another.
Any ideas??

: LATER: I just shortened the url and it worked. Have no idea whether that’s the cure. If you get a problem like this on the site, please let me know. thanks.