Mysql Kayıt Olurken Hata

$kullaniciekle= $vt->prepare("insert into uyeler SET email = :email,
                                                     username = :username
                                                     pass = :pass);

$ekle = $kullaniciekle->execute(array('email'=>$mail,
                                     'username'=>$username,
                                     'pass'=>$pass));

$mail     = htmlspecialchars($_POST["mail"]);
$username =  htmlspecialchars($_POST["username"]);
$pass     =  htmlspecialchars($_POST["pass"]);
$pass2    =  htmlspecialchars($_POST["pass2"]);