please help me in skipjack payment gateway

i am new to payment gateway system and my assignment is integrate skipjack payment. so i have download a class Skipjack.php

that have code below:
Skipjack.php is included in this file and created a object of that class and pass some data that have code below.

1:

print_r($sj->getErrors());

PHP:

above code return empty array
2:

echo $sj->isApproved();

PHP:

above code generate error that ( Notice: Undefined index: szIsApproved in D:\wamp\www\pmp\classes\Skipjacks.php on line 288 )

what i should do?
what is Undefined index: szIsApproved ? how i can fix it? please help me ASAP.

include("Skipjacks.php");
$sj = new Skipjack();
      $sj->setDeveloper(true); // use the development server address
 
      $sj->addFields(array(
              'OrderNumber' => '5',
              'ItemNumber' => 'i5',
              'ItemDescription' => 'Test Item',
              'ItemCost' => '5.50',
              'Quantity' => '1',
              'Taxable' => '0',
              'cvv2'=>"999",
              'AccountNumber' => '4445999922225',
              'Month' => '12',
              'Year' => '2010',
              'TransactionAmount' => '10.00'
      ));
      echo $sj->isApproved();
      if($sj->process() && $sj->isApproved()) {
              echo "Transaction approved!";
      } else {
              echo "Transaction declined!\n";
              print_r($sj->getErrors());
      }

PHP: