I have no idea what PLC FX3g is, but I've done this with AB, Omron, and GE PLC's. For each of them, I had to have a "driver" that would handle the communications. I chose the ActiveX route because I was doing it starting in Visual Basic 6 and that's what worked best.
For the AB and GE I was able to purchase, or was given the ActiveX control that I used. For the Omron PLC I wound up having to write one as the Engineers at Omron failed 13 times to deliver a working ActiveX control. I got fed up and just wrote it myself...took awhile, but it worked!! I imagine that you'll have to do something similar to get yours to work...first see if someone out there has written code that will handle the communication for you. You may have to pay them a bit, but it is WELL worth it if you can start coding your project right away!! If you can't find one, you may have to build your own...if you are not up to that task, contact me and perhaps I can help (for a small fee of course)...but I would recommend doing it yourself, you'll have a MUCH better knowledge of the entire process if you do!! Good luck and let us know how it goes!!