In order to solve the error try uninstalling the utility and then installing it again. Also go to Start > Control Panel > System and Security > Windows Firewall > Allow a program through Windows Firewall and check the box next to Voice2Clear. 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 it still doesn't work it is possible that the Voice2Clear servers might be temporarily down or under maintenance. In this case you will need to wait for a while.
Also, you need to know that some countries (China, Oman, Syria, Turkey, Malaysia, Bahrain, Belize, Iran, Kuwait, Libya, North Korea, Pakistan, Thailand, Tunisia, Vietnam) blocked the VOIP services. If you're living in one of these places, you can't use the software. If none of the above solutions helped, I suggest you use another similar application from Software Informer database.