QSIG dropping calls

Hi all!

I am Asterisk behind a siemens HiPath 4000 since half a year without any problem with EuroISDN. Because I want Name Resolution for the callerid I changed the Protocol on Asterisk (from euroisdn to QSIG) and on HiPath (to PSS1V2).

Normal call creation is working but after a few minutes every call will get dropped (not all at the same time).

Any Ideas?

Regards,
Johannes

Here is the zapata.conf:
#####################

[channels]
language=de
faxdetect=incoming
context=from-pbx
nationalprefix = 00
internationalprefix = 000
;switchtype=euroisdn
switchtype=qsig
pridialplan=unknown
prilocaldialplan=unknown
signalling=pri_cpe
usecallerid=yes
hidecallerid=no
callwaiting=yes
callwaitingcallerid=yes
threewaycalling=yes
transfer=yes
cancallforward=yes
echocancel=yes
rxgain=0.0
txgain=0.0
resetinterval=never
relaxdtmf=yes
busycount=4
overlapdial=yes

group=1
callgroup=1
pickupgroup=1

immediate=no
callprogress=no

callerid=asreceived
channel => 1-15,17-31
channel => 32-46,48-62