asterisk users - Nov 2005 - Problems with some channels on PRI E1 card

Hi list
  I have a problem on a PRI E1 card.
 The connection diagram is:
  [ASTERISK] -- PRI-NET ------------------------------ PRI-CPE -- [NORTELL]
 The problem is:
  When i made a call in channels 17 to 31, there is no voice in any way...
but on channels 1 to 15 i have no problems...
  Any suggestion ???
  my config files
/etc/zaptel.conf
span=1,0,0,ccs,hdb3
bchan=1-15
dchan=16
bchan=17-31


loadzone = us
defaultzone=us

/etc/asterisk/zapata.conf
[channels]

language=en
context=home
switchtype=5ess

signalling=pri_net
usecallerid=yes
hidecallerid=no
callwaiting=yes
callwaitingcallerid=yes
threewaycalling=yes
transfer=yes
cancallforward=yes
callreturn=yes
echocancel=yes
echocancelwhenbridged=yes

rxgain=0.0
txgain=-5.0

group=1
callgroup=1
pickupgroup=1
channel => 1-15
channel => 17-31
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