PDO::errorInfo(): Array ( [0] => 00000 [1] => [2] => )

Bonjour,

j'ai ce code pour l'insertion des données d'un formulaire d'inscription, je ne sais pas d'ou provient l'erreur,
voila mon code :

<?php

function create_sellerid(){
$length = rand(4,14);
$number = "";
for ($i=0; $i < $length; $i++){
$new_rand = rand(0,9);
$number = $number . $new_rand;
}
return $number;
}

if ($_SERVER['REQUEST_METHOD'] == "POST" )
{
if (!$db = new PDO("mysql:host=localhost;dbname=shopdb","root","dani"))
{
die("cannot connect to database");
}


echo "<pre>";
print_r($_POST);
echo "</pre>";





$arr['seller_id']= create_sellerid();
$arr['compname'] = $_POST['compname'];
$arr['usrname'] = $_POST['usrname'];
$arr['email'] = $_POST['email'];
$arr['birth'] = $_POST['birth'];
$arr['phone'] = $_POST['phone'];
$arr['pswrd'] = hash('sha1' , $_POST['pswrd']);


$query = "insert into sellers (seller_id,compname,usrname,email,birth,phone,pswrd) values (:seller_id,:compname,:usrname,:email,:birth,:phone,:pswrd)";

$stm = $db->prepare($query);
if ($stm)
{
$check = $stm->execute($arr);
if (!$check)
{
echo "\nPDO::errorInfo():\n";
print_r($db->errorInfo());
//echo "error";

}
else
{

header("location : index.php");
}
}
}


?>