Have you solved this issue? I got the same or similar problem when an agent logged in and pressed DIAL NEXT, the the audio not a valid extension sound for him, thescreen shows empty information from the lead as if no lead whas taken and no call made hanging up... This is my output.
> Channel SIP/cc466-00da1570 was answered.
== Manager 'sendcron' logged off from 127.0.0.1
-- Executing [8600051@default:1] MeetMe("SIP/cc466-00da1570", "8600051|F") in new stack
== Parsing '/etc/asterisk/meetme.conf': Found
-- Created MeetMe conference 1023 for conference '8600051'
-- <SIP/cc466-00da1570> Playing 'conf-onlyperson' (language 'en')
== Parsing '/etc/asterisk/manager.conf': Found
== Manager 'sendcron' logged on from 127.0.0.1
-- Executing [8600051@default:1] MeetMe("Local/8600051@default-ab36,2", "8600051|F") in new stack
> Channel Local/8600051@default-ab36,1 was answered.
== Starting Local/8600051@default-ab36,1 at default,9,1 failed so falling back to exten 's'
== Starting Local/8600051@default-ab36,1 at default,s,1 still failed so falling back to context 'default'
-- Sent into invalid extension 's' in context 'default' on Local/8600051@default-ab36,1
-- Executing [i@default:1] Playback("Local/8600051@default-ab36,1", "invalid") in new stack
-- <Local/8600051@default-ab36,1> Playing 'invalid' (language 'en')
[Feb 8 17:36:57] WARNING[22179]: file.c:1159 waitstream_core: Unexpected control subclass '-1'
== Parsing '/etc/asterisk/manager.conf': Found
== Manager 'sendcron' logged on from 127.0.0.1
-- Executing [58600051@default:1] MeetMe("Local/58600051@default-eeb7,2", "8600051|Fmq") in new stack
> Channel Local/58600051@default-eeb7,1 was answered.
-- Executing [8310@default:1] Answer("Local/58600051@default-eeb7,1", "") in new stack
-- Executing [8310@default:2] Monitor("Local/58600051@default-eeb7,1", "gsm|20110208-173657_TMK__843") in new stack
-- Executing [8310@default:3] Wait("Local/58600051@default-eeb7,1", "3600") in new stack
== Parsing '/etc/asterisk/manager.conf': Found
== Manager 'sendcron' logged on from 127.0.0.1
== Parsing '/etc/asterisk/manager.conf': Found
== Manager 'sendcron' logged on from 127.0.0.1
== Manager 'sendcron' logged off from 127.0.0.1
== Manager 'sendcron' logged off from 127.0.0.1
== Auto fallthrough, channel 'Local/8600051@default-ab36,1' status is 'UNKNOWN'
-- Executing [h@default:1] DeadAGI("Local/8600051@default-ab36,1", "agi://127.0.0.1:4577/call_log--HVcauses--PRI-----NODEBUG-----0---------------") in new stack
-- AGI Script
agi://127.0.0.1:4577/call_log--HVcauses ... ---------- completed, returning 0
== Spawn extension (default, 8600051, 1) exited non-zero on 'Local/8600051@default-ab36,2'
-- Executing [h@default:1] DeadAGI("Local/8600051@default-ab36,2", "agi://127.0.0.1:4577/call_log--HVcauses--PRI-----NODEBUG-----0---------------") in new stack
-- AGI Script
agi://127.0.0.1:4577/call_log--HVcauses ... ---------- completed, returning 0
== Manager 'sendcron' logged off from 127.0.0.1