Make sure you have Sourcemod/Metamod installed correctly by sending the RCON command meta list
If that works your plugins are likely in the wrong place or out of date, if it doesn't submit a support ticket.
Looking for a game server host known for brilliant 24/7 customer support and quality hardware?
Try a Pingperfect Left 4 Dead server today! https://pingperfect.com/gameservers/l4d-left-for-dead-game-server-hosting-rental.php