I would like help so I can login using cpf or cnpj

<?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['cnpj'])) {
  $loginUsername=$_POST['cnpj'];
  $password=sha1($_POST['senha']);
  $MM_fldUserAuthorization = "usu_nivel";
  $MM_redirectLoginSuccess = "painel.php";
  $MM_redirectLoginFailed = "erro.php";
  $MM_redirecttoReferrer = false;
  mysql_select_db($database_config, $config);

  $LoginRS__query=sprintf("SELECT cnpj, senha, usu_nivel FROM users WHERE cnpj=%s AND senha=%s",
  GetSQLValueString($loginUsername, "text"), GetSQLValueString($password, "text"));

  $LoginRS = mysql_query($LoginRS__query, $config) or die(mysql_error());
  $loginFoundUser = mysql_num_rows($LoginRS);
  if ($loginFoundUser) {

    $loginStrGroup  = mysql_result($LoginRS,0,'usu_nivel');
    $loginStrGroup2  = mysql_result($LoginRS,0,'nivel_empresa');

    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;
    $_SESSION['nivel_empresa'] = $loginStrGroup2;


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