Use
optotrack.dle for establishing the connection. There could be an issue with the network connection or you've incorrectly specified the IP address. You can also try the Optotrack server name instead of IP address. Verify that the Vizard machine and Optotrack server can ping each other. Disable any firewalls/virus scanners on the machines as these may block network communication. Also, take a look at this
video tutorial as it may help.