Someone

The Error page link is:
http://www.forever.co.il/ForEver/

I get.. "Fatal Error - call to undefined function"

this is the source code of index.php (most of the code)

<?php
 include "Def.php";
 include "Conn.php";
 include "Includes/Entrance.php";

 function htmlspecialchars_decode($str, $options="")
  {
   $trans = get_html_translation_table(HTML_SPECIALCHARS, $options);

   $decode = ARRAY();
   foreach ($trans AS $char=>$entity) 
    {
     $decode[$entity] = $char;
    }

   $str = strtr($str, $decode);
   return $str;
  }

...
...
...
?>

in the middle of the page... i get the error here:

          <?php
            if ($mainrsline['adv1on'] == "Is_On")
             {
              echo "<table border=\"1\" cellpadding=\"0\" cellspacing=\"0\" style=\"margin-bottom:5px; border-collapse: collapse; font-family:Arial; font-size:12pt; color:#000000; font-weight:bold\" bordercolor=\"#000000\" width=\"195\" height=\"170\" background=\"".$mainpath."Images/PBox.jpg\"><tr onclick=\"location.href='Advs/Adv1.php'\" style=\"cursor:pointer\"><td width=\"100%\" valign=\"top\" style=\"padding-top: 45px\">".htmlspecialchars_decode($mainrsline['adv1'])."</td></tr></table>";
             }
          ?>

somewhere inside this text, there is a call to the function... :(
don't get it. i call it and i defined it but still, undefined.