Captcha removed from the plugin. Instead security check has been added in Popup Contact form submit page. With this new option Popup Contact form accept submission only from your website domain. It simply reject the submission other then your website domain. After plugin upgrade, Please deactivate and activate the plugin once.

git-svn-id: https://plugins.svn.wordpress.org/popup-contact-form/trunk@939106 b8457f37-d9ea-0310-8a92-e5e31aec5664