[Asterisk-Users] Error on incoming calls

[f.zamboni]

I've a standard debian asterisk installation, with a Juhngans quadBRI 
ISDN board. Sometimes, at unpredictable moments, incoming calls are not 
answered by the asterisk server, with the caller hearing only silence, 
and the only message I can find about this in the logs is the following:

"PRI: received SETUP message for call that is not a new call, wicked!!!"

I've done researchs on the net and I've found other people having the 
same problems, but nobody ever answered them... somebody can suggest me, 
if not where the problem lies, at least where to start to search where 
the problem is?
Thanks to everybody in advance...