When I play call of duty 4 for PS3 I go to multi-player and then go to play online when I try and find a match such as team death match or free-for-all it takes a long time to find a match and when it does it says that the window has been closed. Other times it doesn't go to find a match a window comes up and says "Downloading game settings'.
To solve this:
Go to the online lobby screen where you get the option to select 'Find Game' etc
Switch off the power to your router (don't just disconnect your Ethernet cable).
Press 'X' to exit the 'You have been disconnected... ' screen and then exit the game to go back to the PS3 menu.
Plug your router back in and sign back into the PS Network.