This may be caused by several things. To fix this, you can check the Firewall settings (Windows Firewall or Firewall from a third party tool like an antivirus software) so it doesn't block your software communications. Furthermore, you can check your network connectivity (you should know that is not advise to use VoIP software on wireless networks; if this is your case try to use Ethernet) or try to troubleshoot your IP destination.
