Do you have RSLinx Professional?
Because you’re using a different communication architecture from your previous device, it would be good to cut the possibilities in half by doing a little test:
In RSLinx, browse to your PLC.
Then on the menu, select DDE/OPC and go to Topic Configuration. If your PLC is not in the topics list, add it and make sure it’s pointed to the right path.
Open the OPC Test Client (from the start menu) and connect using RSLinxOPCServer. Add a group and try to add an item. If you can browse online to your point using the test client, then the problem is most likely on the GUI side. If not, AB tech support is your best bet.
~T