yahoo hosting mysql server issues

I have uploaded files on yahoo hosting , but when i open its phpmyadmin credentials of mysql work fine but same credentials not work in code . here is super easy code to connect my

   <?php
$conn = mysql_connect('localhost', 'username','password');
if (!$conn) {
            echo "<p>Could not connect to mysql server </p>\n";
            echo mysql_error();
        }
mysql_select_db('..CMS-2', $conn);
?>

some time it says 500 - Internal Server Error and some time it says message print in code , i have also used mysql instead of localhost but no benefit

Could not connect to mysql server Can't connect to local MySQL server through socket '/tmp/mysql.sock' (46)