Trouble with an IAX Trunk

We recently upgraded our main site to Asterisk 1.4.42 with FreePBX 2.7
We have a remote location running Asterisk 1.4.115285 with FreePBX 2.7

After the main site was upgraded to 1.4.42, the IAX2 trunk between the two locations began to misbehave.

Calls from our main site, to the remote location, work just fine.
Calls from the remote location, to our main site, report that “all circuits are busy”.

I’ve spent the day scouring the web and staring at debug screens, but I’m just not finding anything I can use. Absolutely any suggestions or guidance would be greatly appreciated.

IAX Trunk Config @ Main Site:

[code]Trunk Name: hphc-peer
context=from-internal
host=192.168.60.3
nat=yes
qualify=yes
secret=XXXXX
trunk=yes
type=peer
username=ech-user

User Context: hphc-user
context=from-internal
host=192.168.60.3
qualify=yes
secret=XXXXX
trunk=yes
type=user[/code]

IAX Trunk Config @ Remote Site

[code]Trunk Name: ech-peer
context=from-internal
host=172.30.100.109
nat=yes
qualify=yes
secret=XXXXX
trunk=yes
type=peer
username=hphc-user

User Context: ech-user
context=from-internal
host=172.30.100.109
qualify=yes
secret=XXXXX
trunk=yes
type=user[/code]