Are you using special characters in your password? Try another password with only alphanumerical chars in it or change every /install/template/page.x.php file from
PHP Code:
$server = "mysql://" . $_POST['username'] . ":" . $_POST['password'] . "@" . $_POST['server'] . ":" . $_POST['port'] . "/" . $_POST['database'];
to
PHP Code:
$server = "mysql://" . $_POST['username'] . ":" . rawurlencode($_POST['password']) . "@" . $_POST['server'] . ":" . $_POST['port'] . "/" . $_POST['database'];
Note the rawurlencode().
Also just make sure, the password is correct ;)