Membership Plugin Registration No Longer Functional

I was speaking to @Jack Kitterhing via chat and regrettably we weren't able to come up with a quick solution, so I'm posting to try and determine a fix for my problem. I recently updated my membership plugin with the purchase of a WPMUDEV license and this resulted in my registration page no-longer being functional.

Upon attempting to register, the page refreshes, whereas it formerly would register the user and process them to the account payment page.

http://www.policeteststudy.com/membership?action=registeruser&subscription=1

I've deactivated all modifications and the page is now using the "subscriptionform" shortcode as per @Jack Kitterhing request.

Any help would be greatly appreciated!

Thanks,
Nathan