SYMPTOMS: When trying to join a server, I get a "CD key in use error" and am not allowed into the server.
RESOLUTION #1:This usually happens because there have been some Mods installed on your version of the game. If added mods are suspected and causing unwanted results in game, you can find and delete such mods that will reside in the User Directory > Call of Duty 2 > Call of Duty 2 Data > Main folder. The modded files follow a general file type and extension. Many mods are only one file added into this directory, with the file extension .iwd, the same extension of native necessary files, while some will completely add a new directory in the main folder. With caution, you can delete any files not part of the original install. In addition, the player can DISABLE automatic downloads of these mods with an option in the multiplayer game options. In the multiplayer application, navigate to Multiplayer Options > Allow Downloading > set to NO. When you dispose of all your mods, you should be able to rejoin servers.
RESOLUTION #2: IF YOU HAVE PREVIOUSLY JOINED A MULTIPLAYER GAME SUCCESSFULLY:
The 'CD key in use' error message displays when your serial number is still bound to a previously played server. Your router and the server host will bind your key and cause conflicts when trying to join another game.
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 2 and Call of Duty 4: Modern Warfare. Call of Duty 4 and 2 transmit and receive 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.
IF YOU HAVE NOT PREVIOUSLY JOINED A MULTIPLAYER GAME SUCCESSFULLY (mostly occurs with the App Store releases of Call of Duty 2 and 4):
Please delete the com.aspyr.callofduty4.plist/com.aspyr.callofduty2.plist file from User/Library/Preferences to reset your cd key.
Be advised that if you delete this file, it WILL RESET STATS AND RANKINGS, so we advise that you only do this if you do not mind having these reset.
If you continue to receive this error, open a support ticket with us or email us directly at firstname.lastname@example.org.