I have a registration form with the new google recaptcha widget on it. When a user submits info, we check the validation with javascript and return the problems to the page
your recaptcha render js event should be called only once in the script, your recaptcha code is not valid if grecaptcha.render js event called second time in script. You should have to check your code so it should not call the grecaptcha.render function second time on validation check.
OR
In console, You will see a Uncaught ReferenceError: Recaptcha is not defined error message, which indicates the problem with the reCAPTCHA script. This is caused due to a bad url in the page - http://api.recaptcha.net/js/recaptcha_ajax.js . Google has updated the reCAPTCHA and moved the location of the script to http://www.google.com/recaptcha/api/js/recaptcha_ajax.js .
also check this post
http://www.instructables.com/id/Fix-reCAPTCHA-errors-on-Instructables/
and this post
Uncaught ReferenceError: Recaptcha is not defined