$theValue = function_exists("mysqli_real_escape_string") ? mysqli_real_escape_string($theValue) : mysqli_escape_string($theValue);

Esse é o código:

<?php require_once('Connections/config.php'); ?>
<?php
if (!function_exists("GetSQLValueString")) {
function GetSQLValueString($theValue, $theType, $theDefinedValue = "", $theNotDefinedValue = "")
{
  if (PHP_VERSION < 6) {
    $theValue = get_magic_quotes_gpc() ? stripslashes($theValue) : $theValue;
  }

  $theValue = function_exists("mysqli_real_escape_string") ? mysqli_real_escape_string($theValue) : mysqli_escape_string($theValue);

  switch ($theType) {
    case "text":
      $theValue = ($theValue != "") ? "'" . $theValue . "'" : "NULL";
      break;
    case "long":
    case "int":
      $theValue = ($theValue != "") ? intval($theValue) : "NULL";
      break;
    case "double":
      $theValue = ($theValue != "") ? doubleval($theValue) : "NULL";
      break;
    case "date":
      $theValue = ($theValue != "") ? "'" . $theValue . "'" : "NULL";
      break;
    case "defined":
      $theValue = ($theValue != "") ? $theDefinedValue : $theNotDefinedValue;
      break;
  }
  return $theValue;
}
}
?>
<?php
// *** Validate request to login to this site.
if (!isset($_SESSION)) {
  session_start();
}

$loginFormAction = $_SERVER['PHP_SELF'];
if (isset($_GET['accesscheck'])) {
  $_SESSION['PrevUrl'] = $_GET['accesscheck'];
}

if (isset($_POST['login'])) {
  $loginUsername=$_POST['login'];
  $password=$_POST['senha'];
  $MM_fldUserAuthorization = "nivel";
  $MM_redirectLoginSuccess = "admin/painel.php";
  $MM_redirectLoginFailed = "admin/index.php";
  $MM_redirecttoReferrer = false;
  mysqli_select_db($config,$database_config);

  $LoginRS__query = sprintf("SELECT usuario, senha, nivel FROM lp_users WHERE usuario=%s AND senha=%s",
  GetSQLValueString($loginUsername, "text"), GetSQLValueString($password, "text"));

  $LoginRS = mysqli_query($config, $LoginRS__query) or die(mysqli_error());
  $loginFoundUser = mysqli_num_rows($LoginRS);
  if ($loginFoundUser) {

    $loginStrGroup  = mysql_result($LoginRS,0,'nivel');

    if (PHP_VERSION >= 5.1) {session_regenerate_id(true);} else {session_regenerate_id();}
    //declare two session variables and assign them
    $_SESSION['MM_Username'] = $loginUsername;
    $_SESSION['MM_UserGroup'] = $loginStrGroup;

    if (isset($_SESSION['PrevUrl']) && false) {
      $MM_redirectLoginSuccess = $_SESSION['PrevUrl'];
    }
    header("Location: " . $MM_redirectLoginSuccess );
  }
  else {
    header("Location: ". $MM_redirectLoginFailed );
  }
}
?>

$theValue = function_exists("mysqli_real_escape_string") ?
  mysqli_real_escape_string($theValue) : mysqli_escape_string($theValue);

$theValue = function_exists("mysqli_real_escape_string") ?
  mysqli_real_escape_string($config, $theValue) : mysqli_escape_string($config, $theValue);

mysqli_real_escape_string ( $link ,  $escapestr );

mysql_real_escape_string ( $escapestr );