Cisco 7960 not registering

Hello my fellow users.
I am having trouble with my 7960’s. I have two connected to my network, both are off site so are using port 5060 which has been forwarded through the NAT (yes, I understand the risk). Both have registered, both can make outgoing calls through my trunk but only one can receive calls. Has anyone got any clues?

SIP Version (on 7960): POS3-08-12-00
Latest PIAF with FreePBX (Asterisk Purple)

did you get this working?
I have the same problem?


check my thread
it discuses all the requirements