asterisk users - Sep 2004 - Understanding codecs and transcoder

Hi guys,
This is my first post in this list. I'm newbie with Asterisk and VoIP
technology.

First, this is my scenario:
- Asterisk server (asterisk-1.0.0)
- Cisco router connected to PSTN

I've got redirected incoming call from extension 532x from Cisco to
Asterisk server.

Asterisk server H.323 channel receive the routed call from Cisco, and it
launch the following dial plan:

----[extentions.conf]----
[from-cisco]
exten => 5321,1,Wait,5
exten => 5321,2,DateTime()
exten => 5321,3,Hangup()
-------------------------

------[h323.conf]-------
port=1720
bindaddr=0.0.0.0
disallow=all
allow=g723.1
allow=alaw
allow=ulaw
format=g723sf|wav49|wav
dtmfmode=rfc2833
gatekeeper=DISABLE
context=from-cisco
------------------------

The following lines are the debug.

--- snip snip ---
Asterisk Ready.
*CLI> h.323 debug
H323 debug enabled
*CLI>   == New H.323 Connection created.
        -- Received SETUP message
Urgent handler
    -- Setting up Call
Urgent handler
    --     Call token:  [ip$192.168.1.254:39357/9112]
Urgent handler
    --     Calling party name:  [MyCompany]
Urgent handler
    --     Calling party number:  [8000]
Urgent handler
    --     Called  party name:  [5321]
Urgent handler
    --     Called  party number:  [5321]
Urgent handler
Sending MyCompany to context [from-cisco]
        =-= In OnAnswerCall for call 9112
Launching 'Wait'
Launching 'DateTime'
        answering call
Urgent handler
Parsing A (offset 0) in ABdY 'digits/at' IMp
Set channel H323/ip$192.168.1.254:39357/9112 to write format GSM
Scheduling timer at 160 sample intervals
    -- Playing 'digits/day-2' (language 'en')
Urgent handler
        -- Received Facility message...
        -- Received Facility message...
        -- Sending RELEASE COMPLETE
 -- Call with ImagenSatelital [192.168.1.254] ended abnormally
Spawn extension (from-cisco,5321,2) exited non-zero on
'H323/ip$192.168.1.254:39357/9112'
Scheduling timer at 0 sample intervals
        == H.323 Connection deleted.
Hanging up channel 'H323/ip$192.168.1.254:39357/9112'
oh323_hangup(H323/ip$192.168.1.254:39357/9112)
--- snip snip ---

I don't known why, but the communication was disconnected when Asterisk
launch the DateTime() application. If I try with other application like
a MP3Player(), Voicemail(), SayDigits(), I've got the same negative
result. :(

1- What's happen? What's wrong?
2- Where can I find documentation about how Asterisk works with the
codecs and transcoder?

Thanks very much,
Fede