In includes/modules/payment/authorizenet_aim.php on line 134:

PHP Code:
if (MODULE_PAYMENT_AUTHORIZENET_AIM_TESTMODE == 'Prduction' && (!defined('ENABLE_SSL') || ENABLE_SSL != 'true')) $this->enabled = FALSE; 
Should be:

PHP Code:
if (MODULE_PAYMENT_AUTHORIZENET_AIM_TESTMODE == 'Production' && (!defined('ENABLE_SSL') || ENABLE_SSL != 'true')) $this->enabled = FALSE;