iax_additional.conf not being written


I’ve just installed a clean version of FreePBX on asterisk version 1.4.13.
All appears to be running very smoothly except I am unable to make two IAX peers talk to each other.

IAX2 Trunks are defined on both machines.

On closer inspection, /etc/asterisk/iax_additional.conf is not being written on the machine.
(whereas it is on the 2.2.0 machine)

Anyone know why FreePBX isn’t writing that one config file?
I’ve checked the permissions, they look Ok … where can I look to see potential errors ???