Mentimeter uses a third party service called a Content Delivery Network (CDN) to deliver files to you that are closer to your geographical location.
Sometimes this common practice is blocked by corporate firewalls. If this happens Mentimeter can not function properly.
Contact your IT administrator and ask her/him to unblock. https://d1rp2jn8dkvrz.cloudfront.net
For further help, don't hesitate to contact us at firstname.lastname@example.org