[phpAuction] Errore di installazione

Sto cercando di installare phpAuction GPL versione 3.3 ma arrivati allo step 5 ricevo una segnalazione: Errore 500 internal server error
Di seguito il codice che tenta di eseguire:

define("INCLUDED",1);
    session_start();

    require('../includes/messages.EN.inc.php');

    if($_POST[action] == "next")
    {
        $STEP = 5;
        $_SESSION["STEP"]=$STEP;
        Header("Location: install5.php");
    }

    #// ########################################################
    #// Create database
    #// ########################################################
    mysql_connect($_SESSION['DBhost'], $_SESSION['DBuser'], $_SESSION['DBpassword']);

    /*if($_SESSION[DBaction] == "newdb")
    {
        mysql_create_db($DBdb);
        $DBCREATED = TRUE;
    }
    */

    mysql_select_db($_SESSION['DBdb']);

    $CURRENT = getcwd();
    if($_SESSION[OPERATINGSYSTEM] == "Windows")
    {
        $SQL = str_replace(strrchr($CURRENT,"\\"),"\\sql\\",$CURRENT);
    }
    else
    {
        $SQL = str_replace(strrchr($CURRENT,"/"),"/sql/",$CURRENT);
    }

    include $SQL."dump.inc.php";

    while(list($k,$v) = each($query))
    {
        @mysql_query($v);
    }

    #// Insert some default values into the database
    $query = "UPDATE PHPAUCTIONXL_settings SET
              sitename='".$_SESSION[SETTINGS][sitename]."',
              siteurl='".$_SESSION[SETTINGS][siteurl]."',
              adminmail='".$_SESSION[SETTINGS][adminmail]."'";
    $res = @mysql_query($query);
    if(!$res){
            print "$ERR_001<BR>$query<BR>".mysql_error();
            exit;
        }

    $BG[1]         = "#EEEEEE";
    $FONT[1]     = "#CCCCCC";
    $BG[2]         = "#EEEEEE";
    $FONT[2]     = "#CCCCCC";
    $BG[3]         = "#EEEEEE";
    $FONT[3]     = "#CCCCCC";
    $BG[4]         = "#EEEEEE";
    $FONT[4]     = "#CCCCCC";
    $BG[5]         = "#00CC00";
    $FONT[5]     = "#FFFFFF";


    require "installheader.php";
?> 

Da cosa può dipendere?
Grazie