Ive continuously had the same problem. strangely enough, only at night... i cant help but think that someone used a keygen and got the same serial as me... my version is legit, bought it from game agent.
Ive been in contact with aspyr's support, and not one suggestion has been able to help.
As far as Im concerned too, its a bull**** issue, paid like $70 for the game with CDN exchange and with two babies and work, I only get a little window here and there to escape and play for half an hr.
Ive upgraded to 1.7, installed, reinstalled, uninstalled 1.5 back to 1.7, verified serial, blah blah and problem persists.
Here were some of the useless suggestions that I received from Aspyr:
Thank you for contacting Aspyr Tech Support!
Be sure that your computer is not behind a software or hardware firewall of any kind. This includes firewalls built into routers or other equipment. Aspyr does not support the use of our games from behind a firewall. If it is not possible to disable the firewall you will need to open the ports for Call of Duty 4: Modern Warfare. Call of Duty 4 transmits and receives network traffic on port 28960 (UDP/TCP). The exact details on opening a port is specific to your firewall. For more information check with the firewall documentation or manufacturer.
Another common cause of problems is a poorly configured router or connection sharing solution. If you are using a router, ICS, NAT or a software gateway you may have problems playing on the internet. This is because the router may not be forwarding the correct information back to your machine. It may be possible to get around this problem using port forwarding or DMZ. You can find more information on configuring shared connections for multiplayer gaming at
www.practicallynetworked.com (most of this info is written for PC). Please be aware that like a firewall we cannot actively support using shared connections to play online.
The most common cause of problems though is usually the simplest - an overburdened network stack. By default many computers have protocols the average person doesn't use; things like VPN or NDISWAN. You may want to contact your ISP to find out exactly which protocols you can safely remove. Often times network game problems are resolved by something as simple as removing unused adapters and protocols.
The problem may also be related to the status of your ISP or that of the server. Due to the dynamic nature of the internet and the variable levels of traffic, it is impossible to completely eliminate this error. If you are having persistent problems you may wish to try a different server, or just wait and play a little while later.
Aspyr Tech Support