H.323 error

Hello all !

My situation:
IAX & SIP working fine (SIP to IAX ; IAX to SIP)

I can call from SIP/IAX to H.323 (and reverse) it’s ringing but when I pickup the phone the call is droped.
In Netmeeting: "The person you called is not able to answer"
WellGate 3504A: it’s just droping the call

If I restart (not reload) Asterisk I can call from SIP/IAX to H.323 and it’s working.
If I try to call from H.323 to SIP/IAX it fails.
After it fails like this once, also SIP/IAX to H.323 fails.

What can I do ?