About Arrays in Arduino
For an array of size 7, the indexes start from 0 (ND_MAC[0]) and end at 6 (ND_MAC[6]) as @MikaelPatel commented. 

So the solution to your issue would be changing the condition in for loop to

for(i=0;i&lt;7;i++) //Changed 8 in your code to 7


Here, the loop iterates from i = 0 to 1 &lt; 7 (i.e., till 6)
and it should work. :)