Solved:
The problem was that the Universal Library stops AI DAQ if we attempt to do cbDConfigBit to configure a pin as input or output on the 1608 AUXPORT. Unlike the 1808 there are separate DI/DO pins on the 1608 and there is no need to set the bit on the port to in or out. MCC claim a “Universal Library” but now we have had to put in special handling for different models.