Security Error. Illegal access detected using ccavenue in php

I am successfully redirecting to ccavenue payment gateway but on clicking the cancel button it is showing the error "Security Error. Illegal access detected" in the redirect url page.

This is my redirecturl page:

<?php include('Aes.php');include('adler32.php')?>
<?php
 $workingKey='myWorkingKey';        //Working Key should be provided here.
 $encResponse=$_POST["encResponse"];    //This is the response sent by the CCAvenue Server


$rcvdString=decrypt($encResponse,$workingKey);      
$AuthDesc="";
$MerchantId="";
$OrderId="";
$Amount=0;
$Checksum=0;
$veriChecksum=false;

$decryptValues=explode('&', $rcvdString);
$dataSize=sizeof($decryptValues);

echo "<center>";


for($i = 0; $i < $dataSize; $i++) 
{
    $information=explode('=',$decryptValues[$i]);
    if($i==0)   $MerchantId=$information[1];    
    if($i==1)   $OrderId=$information[1];
    if($i==2)   $Amount=$information[1];    
    if($i==3)   $AuthDesc=$information[1];
    if($i==4)   $Checksum=$information[1];  
}

$rcvdString=$MerchantId.'|'.$OrderId.'|'.$Amount.'|'.$AuthDesc.'|'.$workingKey;
$veriChecksum=verifyChecksum(genchecksum($rcvdString), $Checksum);

if($veriChecksum==TRUE && $AuthDesc==="Y")
{
    echo "<br>Thank you for shopping with us. Your credit card has been charged and your transaction is successful. We will be shipping your order to you soon.";

}
else if($veriChecksum==TRUE && $AuthDesc==="B")
{
    echo "<br>Thank you for shopping with us.We will keep you posted regarding the status of your order through e-mail";


}
else if($veriChecksum==TRUE && $AuthDesc==="N")
{
    echo "<br>Thank you for shopping with us.However,the transaction has been declined.";

}
else
{
    echo "<br>Security Error. Illegal access detected";

}


echo "<br><br>";

echo "<table cellspacing=4 cellpadding=4>";
for($i = 0; $i < $dataSize; $i++) 
{
    $information=explode('=',$decryptValues[$i]);
        echo '<tr><td>'.$information[0].'</td><td>'.$information[1].'</td></tr>';
}

echo "</table><br>";
echo "</center>";
?>

I googled about the issue but was not able to get any solution. How to solve this error..Please give some suggestions regarding the same?

from Security Error. Illegal access detected using ccavenue in php