Local phone Cant receive calls from out of server network

Hi Every one
I have trixbox server and i have just one extension behind NAT .
Aproblem is that extension cant call any other extension in server network , but extensions in server network can call it .
and i try with tow extensions out of server network , works good for 2 side
so the problem in extensions in same network with trixbox server
trixbox server have static ip from ISP
extension1 in the same network with elastix server have DHCP ip 192.168.1.10
firewall off in server router and elastix server , router support QOS VLAN
extension2 behind NAT and firewall
problem now is
extension1 call extension2 OK
extension2 cant call extension1
extnsion3 behind NAT
and extension2 can call extension3 2sides OK
sip_nat.conf
nat = yes
externip =
localnet=192.168.1.0/255.255.255.0
externrefresh = 10
can i find some help plz

the same problem with elastix server

any one can help the same problem in " elastix " , " pbx in a falsh "

give me that massage “circuit-busy
== Everyone is busy/congested at this time (1:0/1/0)”
and this is my network diagram

any ideas