A. This means the IP address and port which is currently setup in the software does not respond.
Check the details entered in Option 2 - LAN Setup and check that the firewall is configured.
B. Check the PC can connect to the VOX400 over the network, enter the IP of the VOX400 into a browser.
C. Check the details in the VOX400 itself, see the full VOX400 manual for more info...