SOLUTION:1.Disabling your firewall
If you have a firewall installed on your computer, make sure it’s not blocking connections to the Activision servers by disabling it. This is something you’ll want to check regardless of the error code you’ve received, so it’s a good place to start. Disabling your firewall will only affect your ability to play MW2. You’ll still be able to browse the Internet and use other applications normally. To do this, go to your firewall software and deactivate the program. Make sure your firewall is not blocking connections to the Activision servers. This will help you get into the game and resolve the issue. If you have a firewall installed on your router, you’ll need to contact your ISP to have them disable it. This will affect all users connected to your network, so make sure to tell them that you need to temporarily disable the firewall.