asterisk users - Jan 2006 - Asterisk doesn't detect answer for some numbers

Hi,
we are running in difficulties with some (rare) numbers: Asterisk doesn't
detect answer and rings indefinitely or drops call with NOANSWER. 
It seems that these numbers are automatic responders.
I tried to debug with 'pri intense debug span 1' but no useful info.
I'm using a Sangoma A102 card with wanpipe beta1-2.3.4, Asterisk is 1.2.1
and Linux is 2.6.9-22.Elsmp.
Line is a PRI E1 in Italy.

With a Digium card, I had not this problem.

I'm looking also for a paid consultant but he/she sould be a really
competent person.

Thanks in advance
Mimmus