Thank you again noiasca, I have confirmed that there is no conflict in the IP's and in-fact both Slaves connect consistently to the Master (see screenshot 1 below, highlights in Yellow and Green).
It seems there is some inconsistency with the UDP part itself. Both Slaves work fine on their own but when both powered up it often happens that one works fine while the other often doesn't receive it's message back from the Master. I have shown this in screenshot 1 in Pink (Slave 1 working fine) and Blue (Slave 2 not receiving the confirmation message back from the Master even though the IP and port is correct).
I almost think it is a timing issue. I have an example in Screenshot 2 where everything is working perfectly, the results seem to be linked to the order and timing with which the individual boards are powered up. More often than not one of the boards does not work but every now and again you can strike lucky as shown here!!
Thank you for the information on COMMON code and the storing of configuration data within the devices themselves. I wasn't aware that that was possible. I will certainly use that in future, thank you again.
