Trying to Debug payment module

Hi
I am trying to debug the secpay payment module to figure out the exact problem
As I see it, I get the error as
"There has been an error processing your credit card. Please try again."
wihch is generated in get_error() in the secpay.php

I appended $_GET parameters and $_POST parameters in the string returned in the function using

$custom_error_message="GET";

       foreach ($_GET as $key => $value)
      {
         //$key = htmlspecialchars( $key );
         //$value = htmlspecialchars( $value );
        $custom_error_message .= $key."->".$value;
     }

$custom_error_message.="POST";

       foreach ($_POST as $key => $value)
      {
         //$key = htmlspecialchars( $key );
         //$value = htmlspecialchars( $value );
        $custom_error_message .= $key."->".$value;
     }


$error=$custom_error_message.MODULE_PAYMENT_SECPAY_TEXT_ERROR_MESSAGE;

Now, what I get in the output is this string:

GET
main_page->checkout_payment
zenid->b445f596fea2366cce9e0ae84337fa44
payment_error->secpay
POSTThere has been an error processing your credit card. Please try again.

My question is how I can get the parameters returned by secpay so that I can find out the root cause of the problem as secpay site states that it returns the
Callback Parameters. How or where can I find the returned values?
Thanks

Anyone please???