asterisk users - Jan 2005 - TDM13B - FXO ports not seeing incoming calls

I seem to have tripped over a problem that just seems plain weird to
me...

I have the TDM card with 1 FXS and 3 FXO interfaces. 
The FXS connects to a modem and EFTPOS terminal, which is working fine.
The 3 FXO ports are connecting to another PBX as internal extensions.

Usually, everything works fine, however, yesterday incoming calls
stopped working. When an extension on the PBX calls one of the three
extensions, it just rings out, with absolutely no output on the asterisk
CLI.

However, when an internal asterisk extension makes an outbound call to
one of the other PBX extensions, it uses the FXO port, and works
perfectly.
    -- Executing Dial("SIP/polycom_l1-c386", "Zap/g10/5586")
in new
stack
    -- Called g10/5586
    -- Zap/126-1 answered SIP/polycom_l1-c386
    -- Hungup 'Zap/126-1'

zapata.conf
-----------
; Analog incoming channel
context => remote
immediate => yes
usecallerid=no
callerid=no
group => 10
signalling => fxs_ks
channel => 126
channel => 127
channel => 128

zaptel.conf
-----------
fxoks=125
fxsks=126
fxsks=127
fxsks=128

Tonight I'll probably just stop asterisk, unload/reload the modules, and
restart asterisk. Usually this is enough to fix things...

If anyone can suggest some debugging to help find the problem, I'd
appreciate it.

Regards,
Adam
-- 
 -- 
Adam Goryachev
Website Managers
Ph:  +61 2 8304 0000                        adam@websitemanagers.com.au
Fax: +61 2 9345 4396                        www.websitemanagers.com.au