membership and authorize.net

I can't seem to get authorize.net to work correctly. I create an account and then I fill out the subscription form. When i press submit it kicks me back out to the register page. No error message or anything. No payments are even registering with authorize.net. I have the login id and transaction key set up, have a md5 hash and ssl. I also made sure plugin and authorize.net were in live mode. Also when i try to use the popup form, it gives a blank page with a return of 0. any help would be great.

I also have custom permalinks set up.

It's a solo site at the moment, set up as a subdirectory of another site. It is Wordpress 3.4 and membership 3.02. no buddypress or anything like that.