[Resolvido] Problemas com POO - Catchable fatal error

Catchable fatal error: Argument 1 passed to User::__construct() must be an instance of BD, none given, called in C:\xampp\htdocs\helpdesk.saviodesigner\public_html\index.php on line 4 and defined in C:\xampp\htdocs\helpdesk.saviodesigner\public_html\lib\Helpdesk\user.php on line 12

porque está mensagem de erro aparece ?