Authorize.net - problem

Here's the URL:
https://aatf-az.com/dev/wordpress/member-signup/

Please feel free to signup for an account to test this.
No need to worry about adding too many users, as I can just delete them.

The two test subscriptions I have setup display after a user signs up, and all of the fields are there, and the proper credit card lights up when the number is put in, but when the Submit button (which by default is a set of a couple credit cards stacked, not very intuitive) is pushed, nothing happens. It's like the button has no action.

I just upgraded to 2.0 from the beta - the beta would act like it was trying to submit the card, then gave an error, but no real detail as to what went wrong, so i figured I'd try the update...really hoping to get this baby functioning.

I am on a PHP4 server.

Thanks for any help!