In order to fix the issue, go to Start > Control Panel > System and Security > Windows Firewall > Allow a program through Windows Firewall and check the box next to Yazak Chat. If you can't find the application 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 the problem persists, upgrade the application to its latest version.