asterisk users - Sep 2005 - oh323 and Asterisk: Calls always hang up

Hi :)

I hope someone can help me (google cannot):
My little asterisk receives calls via h323 from PSTN. I connected a Sipura 
phone to my asterisk. oh323 is installed and calls go into the right context 
but immediately after the phone is picked up a hangup is signalled and the 
call ends :(

This is what I get:
Inbound H.323 call 'ip$213.30.225.5:42873/1893' detected.
Channel OH323/-----@213.30.225.5-0148 created and attached for inbound H.323 
call 'ip$213.30.225.5:42873/1893'.
    -- Executing NoOp("OH323/-----@213.30.225.5-0148", "h323 Call
an
49222299663-99!") in new stack
    -- Executing Playback("OH323/-----@213.30.225.5-0148",
"tt-monkeysintro")
in new stack
Channel OH323/-----@213.30.225.5-0148 answered.
    -- Playing 'tt-monkeysintro' (language 'en')
Call 'ip$213.30.225.5:42873/1893' cleared.
    -- H.323 call 'ip$213.30.225.5:42873/1893' cleared, reason 24 (Call
ended
with Q.931 cause)
Sep 14 10:30:42 WARNING[14895]: file.c:970 ast_waitstream: Unexpected control 
subclass '5'
Call 'ip$213.30.225.5:42873/1893' with owner has already been cleared
(2).
Call 'ip$213.30.225.5:42873/1893' has been hungup.
    -- Hungup 'OH323/-----@213.30.225.5-0148'
Call 'ip$213.30.225.5:42873/1893' without owner has already been cleared
(2).

Any ideas?

Thanks and kind regards,
Hauke