All Circuits Are Busy

We are running FreePBX version 2.7.0-10 with Asterisk and Elastix 2.0.0-62. The issue we are having is the call treatment and disposition. When a wrong number is dialed, the outbound carrier is returning the proper cause codes. However, the users on the PBX are reporting they keep getting an “All Circuit Are Busy” message. Is there a known bug out there relating to this issue?

In Module Admin, download and install Route Congestion Messages
This module will allow you to define your own messages for the following HANGUPCAUSES:
18 - No User Responding, or SIP 408 Request Timeout
19 - No Answer From The User, or SIP 480 Temporarily Unavailable, SIP 483 To Many Hops
28 - Address Incomplete, or SIP 484 Address Incomplete