migration of 14.2 FDS app back to 12.3

I have a fairly extensive application built in 12.3.

To add FDS to this I started with 14.2, replaced the logging with RTT and I know I'll have the change the FDS calls.

This builds fine in 14.2 for pca10040 and runs OK.

However, I was not expecting this error when building 12.3:

In file included from ../../../../../../components/boards/boards.h:43:0,
                 from ../../../../../../components/boards/boards.c:40:
../../../../../../components/drivers_nrf/hal/nrf_gpio.h:67:2: error: #error "Not supported."
 #error "Not supported."

This seems to indicate a problem with boards which is odd because pca10040 is supported in bother cases.

Any suggestions please?