Modbus TCP

[pilot123]

Further to my post on 19 April, I have tried simulating the Master to a hardware slave and vice versa to no avail.
I have ran my hardware setup again using 2 BL0080 boards as Master and Slave devices using the Eth Wiz 5500 boards / BL0106 Click adaptor boards both connected to Port A.
On the Master I am using a BL0145 Switch Board connected to Port C using Bit 7 as my Switch, and on my slave a BL0117 Prototype Board to wire my LED to Port C Bit 0.
I have connected my Master and Slave to a Cisco Switch, and I have programmed Port 5 on the switch as a Monitor Port so that I can monitor the traffic with Wireshark.
I can ping both devices from my PC Master IP 192.168.100.20 Slave IP 192.168.100.10. When I press the switch on the Master a TCP Port 502 message is sent to the Slave and the Slave responds with a TCP Port 502 ACK Reply. But it appears looking at the Wireshark messages that the actual Modbus message is not being sent in the TCP packet as LEN = 0, which I think means there is no payload being sent
I have attached a Screenshot of the Wireshark screen, and a copy of my programs.
Any help would be appreciated as I am stuck?

Thanks.