### zaptel.conf ###
defaultzone=us
fxsks=3-4

### zapata.conf ###
[channels]
language=es
context=default
usecallerid=yes
hidecallerid=no
callwaitingcallerid=yes
echocancel=64
echocancelwhenbridged=yes
echotraining=800
relaxdtmf=no
busydetect=yes
busycount=6
rxgain=0.0
txgain=0.0
group=1
callgroup=1
pickupgroup=1
immediate=no
signalling=fxs_ks
faxdetect=both
context => fabrica
channel => 4
context => casa
channel => 3


### Loading zaptel ###
Module 0: Not installed
Module 1: Not installed
Module 2: Installed -- AUTO FXO (FCC mode)
Module 3: Installed -- AUTO FXO (FCC mode)
Found a Wildcard TDM: Wildcard TDM400P REV E/F (4 modules)


### Loading asterisk after loading zaptel ###
  == Parsing '/etc/asterisk/zapata.conf': Found
Feb 28 11:29:06 WARNING[7162]: chan_zap.c:778 zt_open: Unable to specify channel 4: No such device or address
Feb 28 11:29:06 ERROR[7162]: chan_zap.c:6239 mkintf: Unable to open channel 4: No such device or address
here = 0, tmp->channel = 4, channel = 4
Feb 28 11:29:06 ERROR[7162]: chan_zap.c:9191 setup_zap: Unable to register channel '4'
Feb 28 11:29:06 WARNING[7162]: loader.c:345 ast_load_resource: chan_zap.so: load_module failed, returning -1
  == Unregistered channel type 'Tor'
  == Unregistered channel type 'Zap'
Feb 28 11:29:06 WARNING[7162]: loader.c:440 load_modules: Loading module chan_zap.so failed!



(If I reboot the server, asterisk starts normally but line attached to channel 4 is busy, pluggin the line directly to a regular phone works)