[Asterisk-Users] Echo on one E1 line, but not the other

[Asterisk]

We're rolling out Cisco 7940 phones, linked to *, which is running a TE405p
EuroISDN.

We have 2 ISDN lines, one we had for testing, and one for general (40+
users) use.

During the testing phase, we had 10 phones linked to the second ISDN line,
and there were no problems with echo at all. Lucky me. However, since we
have started rolling out, we've had quite loud complaints that there is "a
terrible echo". If I direct my 7960 to use the primary line, there is an
echo. If I use the second line (dialling the same external number) there is
no echo at all.

What could be the issue ? I have noticed on the primary line there is a
"detected rx/tx on channel xx, echo cancellation disabled" (or something
like that. Is this the cause ? We have several fax / modems going through
the line - should I always dedicate a channel to them ?

I've included my zaptel.conf and zapata.conf file below. Any help / comments
appreciated.

#
# Zaptel Configuration File
#
# This file is parsed by the Zaptel Configurator, ztcfg
#

span=1,1,0,ccs,hdb3,crc4
bchan=1-15,17-31
dchan=16

span=2,0,0,ccs,hdb3,crc4
bchan=32-46,48-62
dchan=47

span=3,2,0,ccs,hdb3,crc4
bchan=63-77,79-93
dchan=78

span=4,0,0,ccs,hdb3,crc4
bchan=94-108,110-124
dchan=109

loadzone=uk
defaultzone=uk

#############################################

;zapata.conf

[general]

[trunkgroups]

[channels]
musiconhold=default
language=en
rxwink=300		; Atlas seems to use long (250ms) winks
usecallerid=yes
hidecallerid=no
callerid=asreceived
callwaiting=yes
usecallingpres=yes
callwaitingcallerid=yes
useincomingcalleridonzaptransfer=yes
threewaycalling=yes
transfer=yes
cancallforward=yes
callreturn=yes
echocancel=yes
echocancelwhenbridged=yes
echotraining=yes
echotraining=800
;relaxdtmf=yes
rxgain=0.0
txgain=0.0
;callgroup=1
;pickupgroup=1
;adsi=yes

context=isdn32-b
pridialplan=unknown
group=1
signalling=pri_cpe
switchtype=euroisdn
channel=1-15,17-31

context=meridian-b
group=2
signalling=pri_net
switchtype=euroisdn
channel=32-46,48-62

context=isdn32-a
pridialplan=unknown
group=3
signalling=pri_cpe
switchtype=euroisdn
channel=63-77,79-93

context=meridian-a
group=4
signalling=pri_net
switchtype=euroisdn
channel=94-108,110-124