LG PLC - RNET Network

I am busy setting up an LG PLC to run some remote smart I/O also LG using RNET, I get 6 units to work but as soon as the 7th one is added the network start losing comms with some of the other I/O units! Poling time has been changed from 20mS to 100mS with no change in the behavior of the network, HS link parameters has been verified as well as the physical network installation - even tried to adjust the network resistance by adding more resistors, any other sugestions will be gr8