IAX2 Trunk between systems

Hi There,

I have an IAX2 trunk configured between two remote systems. All works as normal for internal calls (extension to extension) but If I take a call originating at one system and transfer it to the other system I only get audio in one direction.

My trunks are configured as follows.

username=System2
secret=XXXXXXXXXX
host=XXX.XXX.com
type=friend
context=from-internal
qualify=yes
qualifyfreqok=25000
transfer=yes
trunk=yes
forceencryption=yes
encryption=yes
auth=md5
requirecalltoken=no
disallow=all
allow=ulaw&g729
canreinvite=no

and the converse on the other box.

Any help would be greatly appreciated.