Error on member ship plugin with authorize.net

I am getting the error "There was an unknown error encountered with your payment. Please contact the site administrator." When I click to process a subscription through the membership plugin on authorize.net. I assume it is because the Register page is not coming up under the https ( I do have an ssl installed) Can I please get some help processing these? I have three levels and none of them are set to Serial, all to Finite. Thanks!