The Net-ENT isn't a PLC, that is just an Ethernet to serial converter. Can you find out what PLC it is connected to? I've never worked with a Net-ENI and AdvancedHMI, but try this instead:
EthernetIPforPLCSLCMicroCom1.Write("C5:0.ACC", 1)
See if that writes a 1 to your counter accumulated value.