Why can't I test signup through another user?

http://flyairline.co/OPE/test-signup/

We are using the WPMU Membership Plugin.

For the life of me, I cannot test signup through any of the subscriptions we've made. Once the signup form is filled and submitted, the page will just refresh. Nothing happens.. no new user account is made.

What am I doing wrong here?

Thanks for the plugin to disable notifications. It has helped. Perhaps you can help me here too.