Unable to forward voice frame

This happens on Zap lines when user dials incorrect number.

Far end sends:

< Message type: PROGRESS (3)
< [08 02 84 81]
< Cause (len= 4) [ Ext: 1  Coding: CCITT (ITU) standard (0) 0: 0   Location:
Public network serving the remote user (4)
<                  Ext: 1  Cause: Unallocated (unassigned) number (1), class =
Normal Event (0) ]

http://lists.digium.com/pipermail/asterisk-users/2005-July/108709.html