It seems that the urls //https://admin.recaptcha.net/recaptcha/createsite// and //http://recaptcha.net/apidocs/captcha/client.html// have both been deactivated by google.
Admin is now available in https://www.google.com/recaptcha/admin/
API is now at http://www.google.com/recaptcha/api

eZComments settings should be updated to reflect this change.