To use reCAPTCHA you must get an API key

I am using the CB AntiSpam plugin to display reCAPTCHA on my CB User Registration page. The reCAPTCHA image displays fine but when users click submit they get a plain white page that says

"To use reCAPTCHA you must get an API key from www.google.com/recaptcha/admin/create "

I have quadruple checked to make sure that the private and public key have been properly entered into the Captcha - ReCaptcha plugin in Joomla.

If I disable the CB AntiSpam plugin, I don't get the reCAPTCHA image but the rest of registration seems to run fine.

What am I missing?

I'm running Joomla 3.4 with CB 1.9.1

As you're on CB 1.x you're using an older CB AntiSpam, which is using v1 reCaptcha API. Google has discontinued v1 API for new keys. So you've a v2 key and trying to use it with v1 API. It's not going to work. You'll need to upgrade to CB 2.x and update CB AntiSpam for v2 reCaptcha usage.