Have you had this problem with other games.
I don't know too much about Internet things but trial and error seems to work for me; try unplugging and replugging your net line, try the network settings menu on the XMB, try anything.
I some times have problems with connection and it turns out to be that my internet cable is not fully in the back of the PS.
Maybe someone here can help if they've had the same thing happen to them.
Good luck.
