Two issues.
1. The error message *you* are seeing is a result of a display bug.
2. The *cause* of the condition is that your server is missing a critical component.
Line 86:
Code:
if ($this->enabled && !function_exists('curl_init')) $messageStack->add_session(MODULE_PAYMENT_AUTHORIZENET_AIM_TEXT_ERROR_CURL_NOT_FOUND, 'error');
The only reason it would be giving you the error message you describe is if your server doesn't have CURL compiled into PHP.
CURL with SSL is required to be compiled into PHP on your server in order for Zen Cart to connect to some external resources such as Authorize.net.
Fix your CURL problem and the error will go away. You'll have to talk to your hosting company to deal with that.
To test CURL support, try pointing your browser to this address:
http://your_site.com/your_zen_cart_f...test.php?aim=1
(replacing your_site.com and your_zen_cart_folder_name as appropriate)
And, we'll fix the bug causing the wrong message to display, for the next version.