in the WA_eCart/Adv_CO_Scripts/AuthNet_PHP.php file locate the following code:
curl_setopt($ch, CURLOPT_POST,1);
and add the following on a new line after it:
//curl_setopt($ch, CURLOPT_PROXYTYPE, CURLPROXY_HTTP);
curl_setopt($ch, 101, 0);
curl_setopt($ch, CURLOPT_PROXY,"http://proxy.shr.secureserver.net:3128");
curl_setopt($ch, CURLOPT_TIMEOUT, 120);