Upgrade reCAPTCHA to use version 2.0.
Google is sunsetting reCAPTCHA v1 and as of March 2018 all v1 API calls will no longer work.
In response to this End of Life announcement, Liferay Portal 6.2 EE has been updated to include reCAPTCHA version 2. Liferay Digital Enterprise already utilizes reCAPTCHA v2.
See https://customer.liferay.com/documentation/knowledge-base/-/kb/1984814 for further information and actions required to be made after installing this fix.