In order to fix the issue, try rebooting your PC and running the game using Administrator rights. If it doesn't help, go to Start > Control Panel > System and Security > Windows Firewall > Allow a program through Windows Firewall and check the box next to Combat Arms. If you can't find the game in the "Allowed programs and features" window, press the "Allow another program" button, navigate to the installation directory, select the executable file and press Add. After that, from the Advanced Settings select Inbound Rules > New Rule. Check the Port box, click Next, select All local Ports and follow the self-explained steps. Also, make sure that your security program doesn't block the connection. If it still doesn't work, uninstall the game, download and install the upgraded version of the client. This should fix it.