asterisk users - Mar 2006 - can't get TDM400P to answer

Hi all,

I can't figure out why my TDM400P (with one FXO plugin) won't answer any
calls. There are no messages in the Asterisk console when a call is 
placed to the FXO line from the PSTN. Any suggestions would be most 
appreciated.

The wctdm and zaptel modules are loaded:
[root@steerpike asterisk]# lsmod | grep wc
wctdm                  37952  0
zaptel                189700  1 wctdm

The green LED on the input connector is lit. ztcfg says:
...
Channel map:
Channel 04: FXS Kewlstart (Default) (Slaves: 04)
1 channels configured.


My zaptel.conf is:
fxsks=4
loadzone=us
defaultzone=us

and zapata.conf is:
[channels]
group=1
context=tdm400p-inbound
signalling=fxs_ks
echocancel=yes
echocancelwhenbridged=yes
relaxdtmf=yes
rxgain=1.5
txgain=1.5
immediate=no
busydetect=no
callprogress=no
musiconhold=default
usecallerid=yes
callerid=asreceived
channel => 4

The relevant sections of extensions.conf are:

[tdm400p-inbound]
exten => s,1,Ringing()
exten => s,2,Goto(MainMenu,s,1)
exten => s,3,Hangup;
...
[MainMenu]
exten => s,1,Wait,3                     ; ring for 1 second
exten => s,2,Answer                     ; answer
exten => s,3,Background,welcome
etc...

The TDM400P power connector is attached, even though it isn't supposed 
to be required for FXO modules.

Any ideas?

- Mike