PHP user registration script

<?php
//We connect to the database
$host="localhost"; // Host name
$username="root"; // Mysql username
$password="testdbpass"; // Mysql password
$db_name="test"; // Database name

// Connect to server via PHP Data Object
$dbh = new PDO("mysql:host=localhost;dbname=test", $username, $password);
$dbh->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);

//Validation


CRYPT_BLOWFISH or die ('No Blowfish found.');

//This string tells crypt to use blowfish for 15 rounds.
$Blowfish_Pre = '$2y$17$';

// Blowfish accepts these characters for salts.
$Allowed_Chars =
'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789./';
$Chars_Len = 63;


$salt = "";

for($i=0;$i<45 ;$i++)
{
    $salt .= $Allowed_Chars[mt_rand(0,$Chars_Len)];
}
$bcrypt = $Blowfish_Pre . $salt;

$password = crypt($_POST['password'] , $bcrypt) ;

// Insert statements with PDO

try {
        $query = $dbh->prepare("INSERT INTO `users` (username, email, fname, lname, password)
                               VALUES (:username, :email, :first, :last, :password)");

        $query->execute(
                        array(
                        'username'  => $_POST['username'],
                        'email'     => $_POST['email'],
                        'first'     => $_POST['fname'],
                        'last'      => $_POST['lname'],
                        'password'  => $password
                        ));
    }

    catch (PDOException $e) {
        error_log($e->getMessage());
        die($e->getMessage());
    }

    $dbh= null;

    ?>

<html>
    <body>
        <p>
            Thank you for registering your account. Please wait for administrator approval before doing anything else. Thank you - System Administrator.
        </p>
    </body>
</html>