I also need a few questions answered to make sure im doing everything right!
1. CoD 1 is the game your having trouble with?
2,Are you using GameSpyArcade to join or what?
3.After installing 1.5 did you try renentering your cd key?
Ok i need to know that information
-NOTE-
Ok now if your friend or the guy who gave you game has registered that cd key in his player name, then no you cant until he logins to his account and deletes his account for the game!You cant have 2 accoutns with same CD Key!
I found this article at Activision Support also!
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, as well as programs like Zone Alarm, Black Ice, and the integrated firewall in Windows XP. Activision 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. Call of Duty transmits and receives network traffic on port 28960 using both TCP and UDP. 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. 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.