Go to Start > Control Panel > System and Security > Windows Firewall > Allow a program through Windows Firewall and check the box next to Visatell. 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 and open the executable file. 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 antivirus program doesn't block the connection. If the problem is not solved, reinstall the program.