Many times you have more than one network connection on a PC. You might have a wired connection to the company LAN with internet access and another connection, wired or wireless, to a private LAN where your Yokogawa devices are connected. Sometimes windows routing gets confused, and when you try to connect to a device on a private or local network (an IP address of 10.0.0.0 - 10.255.255.255, 172.16.0.0 - 172.31.255.255, or 192.168.0.0 - 192.168.255.255), the computer tries to send traffic out the wrong network connection.
You can prevent this by installing a “Persistent Route” on your computer. Read this article on Microsoft's website: http://technet.microsoft.com/en-us/library/cc978475.aspx.
Then use the "Route -p add ....." command as described on this Microsoft website: http://www.microsoft.com/resources/documentation/windows/xp/all/proddocs/en-us/route.mspx?mfr=true. You can use the command “route print” at the command prompt to see if a persistent route has been installed properly.