asterisk users - Aug 2005 - fax <--> grandstream 286 <--> asterisk <--> pstn

Hi all,

Im having problems using a fax machine conected trough a grandstream
286 sip ATA, it must be able to send and recive fax from pstn, but fax
always ends with communication errors 252/244/232 and others.

Im using alaw/ulaw codes on pass trough mode, also have tried asterisk
faxdetection, nvfaxdetect, disable echo cancellation by hand always
with same results.

Grandstream ATA is using firmware version 1.0.6.7

Im using efax with a serial modem, to send faxes to asterisk, hopping
it forwards them to the fax machine, here it the log

efax -d /dev/ttyS0 -o f -t 913664813 sun480-boot
efax: Wed Aug  3 16:37:35 2005 efax v 0.9a-001114 Copyright 1999 Ed Casas
efax: Wed Aug  3 16:37:35 2005 efax v 0.9a-001114 Copyright 1999 Ed Casas
efax: 37:35 compiled Dec  2 2004 14:28:56
efax: 37:35 opened /dev/ttyS0
efax: 37:36 using V1.002.C04-K56_DLS in class 1
efax: 37:36 dialing 913664813
efax: 38:00 connected
efax: 38:01 received UNKNOWN
efax: 38:01 Warning: bit-reversed HDLC frame, reversing bit order
efax: 38:01 received CSI - answering ID
efax: 38:01 remote ID ->            913664813
efax: 38:02 received DIS - answering capabilities
efax: 38:02 remote has no document(s) to send, and can receive
efax: 38:02 local   196lpi 14.4kbps 8.5"/215mm  any   1D    -     -  0ms
efax: 38:02 remote  196lpi 14.4kbps 8.5"/215mm  any   2D ECM-64   -  0ms
efax: 38:02 session 196lpi 14.4kbps 8.5"/215mm  any   1D    -     -  0ms
efax: 38:02 sent TSI - caller ID
efax: 38:04 sent DCS - session format
efax: 38:07 sent TCF - channel check of 2700 bytes
efax: 38:11 received DCS - session format
efax: 38:11 local   196lpi 14.4kbps 8.5"/215mm  any   1D    -     -  0ms
efax: 38:11 remote  196lpi 14.4kbps 8.5"/215mm  any   2D ECM-64   -  0ms
efax: 38:11 session 196lpi 14.4kbps 8.5"/215mm  any   1D    -     -  0ms
efax: 38:11 sent TSI - caller ID
efax: 38:12 sent DCS - session format
efax: 38:16 sent TCF - channel check of 2700 bytes
efax: 38:19 received DCS - session format
efax: 38:19 local   196lpi 14.4kbps 8.5"/215mm  any   1D    -     -  0ms
efax: 38:19 remote  196lpi 14.4kbps 8.5"/215mm  any   2D ECM-64   -  0ms
efax: 38:19 session 196lpi 14.4kbps 8.5"/215mm  any   1D    -     -  0ms
efax: 38:19 sent TSI - caller ID
efax: 38:21 sent DCS - session format
efax: 38:25 sent TCF - channel check of 2700 bytes
efax: 38:28 received DCS - session format
efax: 38:28 Error: no command/response from remote
efax: 38:28 sent DCN - disconnect
efax: 38:32 failed -> sun480-boot
efax: 38:32 done, returning 3 (invalid modem response)

and the asterisk log

 -- Starting simple switch on 'Zap/4-1'
 Aug  3 16:37:14 NOTICE[16135]: chan_zap.c:5377 ss_thread: Got event 2
(Ring/Answered)...
 -- Executing Answer("Zap/4-1", "") in new stack
 -- Executing NVFaxDetect("Zap/4-1", "4|dt") in new stack
 Aug  3 16:37:16 NOTICE[16135]: app_nv_faxdetect.c:215
nv_detectfax_exec: Redirecting Zap/4-1 to fax extension
 -- Executing Dial("Zap/4-1", "SIP/gw3") in new stack
 -- Called gw3
 -- SIP/gw3-4ffd is ringing
 -- SIP/gw3-4ffd answered Zap/4-1
 == Spawn extension (linea-fax, fax, 1) exited non-zero on 'Zap/4-1'
 -- Hungup 'Zap/4-1'


Does anyone know what could be happening? any suggestions?
Tell me if more info is needed.

Thanks,
Jaime.