[kh99]

So just to make sure, this doesn't happen if you disable this mod? I guess it works if you choose no human verification? What happens if you try the other hv types? I would think maybe it had something to do with contacting google to verify the response, but the test in the admincp uses the same code as when it's being done by a user (well, that's what I tried to do, anyway), and that didn't show any errors.

Edit: oh, maybe it's an apache mod that doesn't like the looks of the rCaptcha response in the post data, or something like that. I don't know much about web site admin, but I've seen other people mention mod_security when they get an error like this.