I had this problem a while back because I haven't worked with my code in a while. They main problem I had was that I needed to choose the correct IP on Arduino side and port number - i used 192.168.1.77 with port 80 as my Arduino - and you need to create a visa via NI MAX which is the Arduino's IP AND Port number. In my later code, I've wrote an auto forumate Visa script.
This is a link to a drop box file which has the VI I use to make a TCP VISA. I found the code somewhere in the forums and I changed it to fit my need. Basically, the only thing you need to do is add a host name (xxx.xxx.xxx.xxx) and it will create that as a VISA working on port 80. I use this VI to check if the IP being entered is in the VISACONF.ini file. If the VISA exisits, then the second loop skips over and doesn't create another Visa, if it's not, then the second loop creates a VISA and stores it in VISACONF.ini. Hope it helps.
https://dl.dropboxusercontent.com/u/60210515/Create%20VISA.vi
Again, this code works for me, I made it for one of my aplications and tried to release the base of my code - quite horribly from the looks of it - and Sammy_K has released LIFA code that works over eathernet and can be found https://www.labviewhacker.com/doku.php?id=libraries:linx:linx. It's called LINX and I personally havent worked with it, but I'm assuming its well documented and be worked with easier than my code.
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