According to Activision's support knowledge base error 33 is due to packet (data) loss when downloading- in other words, some of the data is going astray while in transit to you.
They recommend making sure the following ports are open in your router in Port Forwarding: 3658, 3478, 3074, 3075 (UDP) and ports 80, 443, 5223 (TCP). One alternative, if you have a static IP address set up for the PS3, is to put that address into the router's DMZ. If all else fails, try a direct connection to the modem, bypassing the router altogether- it's possible the router itself may not be completely compatible for the PS3 and the game.