no answer after dial

HI,
I have 2 A-800Ps plugged in a PC. I failed to use same channels to make a call to PSTN. It shows it can't establish connection after dial command issued. Below is the log. Actually, the call is established as I can hear voice from the called party but the softphone is still showing ringing. It seems the TDM card can't get an answered signal from PSTN. After 15 seconds, the call dropped because there is no answered signal. I want to know how to handle the problem? Is it related to settng?

[Nov 23 01:23] VERBOSE[5722] logger.c: -- Executing
[91872800@internal-admin] Dial("SIP/2001-0a0240c0",
"Zap/2/1872800|15") in new stack
[Nov 23 01:23] DEBUG[5722] dsp.c: dsp busy pattern set to 0,0
[Nov 23 01:23] DEBUG[5722] chan_zap.c: Dialing '1872800'
[Nov 23 01:23] DEBUG[5722] chan_zap.c: Deferring dialing...
[Nov 23 01:23] VERBOSE[5722] logger.c: -- Called 2/1872800
[Nov 23 01:23] DEBUG[5722] chan_zap.c: Done dialing, but waiting
for progress detection before doing more...
[Nov 23 01:23] VERBOSE[5722] logger.c: -- Nobody picked up in 15000 ms
[Nov 23 01:23] VERBOSE[5722] logger.c: -- Hungup 'Zap/2-1'
[Nov 23 01:23] NOTICE[5722] cdr.c: CDR on channel 'Zap/2-1' not posted
[Nov 23 01:23] VERBOSE[5722] logger.c: -- Executing
[91872800@internal-admin] Hangup("SIP/2001-0a0240c0", "") in new
stack
[Nov 23 01:23] VERBOSE[5722] logger.c: == Spawn extension
(internal-admin, 91872800, 2) exited non-zero on 'SIP/2001-0a0240c0'
[Nov 23 01:23] VERBOSE[5722] logger.c: -- Executing
[h@internal-admin] Hangup("SIP/2001-0a0240c0", "") in new stack
[Nov 23 01:23] VERBOSE[5722] logger.c: == Spawn extension
(internal-admin, h, 1) exited non-zero on 'SIP/2001-0a0240c0'

hello, please tell us your confs and we are able to help you. i think, maybe, something is wrong with confs such as sip.conf, extensions.conf and zapata.conf. again, please show us details .
rgs!
james.zhu