same thing happened to me. It has something to do with your router settings. Most likely ports arent open.
I tried opening the ports in activisions support knowledge base and still didnt work. What I do to get around this is just plug my ethernet cable directly into the modem. It works everytime.
This is the article from the activision support knowledge base:
This is caused by Packet Loss, which means a file or data was lost as the server was sending it to the client.
If you are using a router try the following:
-Set port forwarding on your router to your Playstation 3. Call of Duty 4: Modern Warfare uses ports 3658, 3478, 3074, 3075 (UDP) and ports 80, 443, 5223 (TCP).
-Place your Playstation 3 into the DMZ of your router.
-If both fail disconnect your router and try the game. If it works regularly at this point something about your router may not be completely compatible with the specific needs of this game. Check with your router manufacturer for additional steps that may need to be done to resolve the issues you are seeing.
NOTE:If setting port forwarding or DMZ helps your gameplay you may wish to assign your Playstation 3 a static IP address inside your home network, this will help ensure that the configurations you made do not need to be redone.
NOTE: Many broadband internet modems are coming with routing capability built in. Please contact your internet service provider to determine if your internet modem has an integrated router, if it does they should be able to assist you with the steps above for setting up a router.
I hope that helps.
Actually he may be having the same issue as I have been seeing. I get no errors at all. When I try to play online as soon as I select find game or set up private match it will lock up my PS3 and I have to manually power it down by pressing and holding the power button down until it shuts off. Happened three separate times so far. Gave up on it until I either hear back from support or they "patch" it.
I played COD 4 for about four hours over the weekend and didn't have any problems. The game ran great even a couple of matches where I only had 2 bars. I only got into one hacked lobby. One guy had infinite noob tubes and the other had infinite rpg's. The one thing I noticed about COD 4 that I didn't realize or had forgotten about is everyone runs with martyrdom.
Tryed to play Black Ops last night and as usual it ran like sh!t. Played one match then turned it off and played some MW3 until the servers went down.