[Asterisk-Users] Random Zap Channel Drops to SIP

[asterisk fpf]

Asterisk Version: 1.2.9.1
Zaptel Version: 1.2.6
LibPri Version: 1.2.3

Hey List,

we are running an asterisk server in connection with an octopus 
telephone system. I have expired some random drops of zap channels
bridged to SIP Telefones ( snom 190 ). Asterisk Messages shows something 
like that:

Jun  9 09:32:33 WARNING[3207] res_features.c: Bridge failed on channels 
SIP/fon01-6945 and Zap/32-1

This is my zapata.conf :

switchtype=qsig
pridialplan=unknown
prilocaldialplan=unknown
internationalprefix=00
nationalprefix=0
usecallingpres=yes
callwaitingcallerid=yes
echotraining=500
echocancel=yes
echocancelwhenbridged=no
transfer=yes
cancallforward=yes
callreturn=no
busydetect=no
threewaycalling=yes
callprogress=no
overlapdial=yes
callwaiting=no
usecallingpres=yes
immediate=no
usecallerid=yes
hidecallerid=no
restrictcid=no
callerid=asreceived
language=de
rxgain=2.5
txgain=-0.5
group=2
signalling=pri_net
channel => 32-46,48-62

I Hope someone could help in this case. Thank you in advice

Greetings,
 Michael