asterisk users - Aug 2003 - ISDN BRI outgoing call instant hangup

Hello everybody,

I have managed to setup an asterisk system with one hfc based isdn bri 
card. In addition i use a cisco ubr 924 as an h323 gateway, and the 
gnugk gatekeeper. I can call from h323 terminals and connect to the demo 
  context. I can also call any h323 terminal. Incoming calls through 
isdn get to the demo context and i can even get connected to my h323 
terminals through an exten.

When i attempt to Dial an outgoing call from my h323 terminals i can see 
that asterisk dials out through the modem channel, but instantly 
hangups. As a test i call my second phone number and some times i can 
here that phone ringing for a momment just before the modem hangs up.
Asterisk reports that the modem hungup.

Any thoughts;

What data can i supply to you to aid in debugging???


Thanks in advance.