Hi Bruno,
Your best would be to add one of these to your route script:
http://www.kamailio.org/dokuwiki/doku.php/core-cookbook:1.5.x#error_route
It would allow you to log the precise nature of the syntax errors in the
malformed SIP messages you are receiving and to further isolate the
problem from there.
Please note that this feature no longer exists in Kamailio/sip-router >=
3.0, and is superseded by the sanity_check() routine. However, it does
work in 1.5.x.
Cheers,
--
Alex Balashov - Principal
Evariste Systems LLC
1170 Peachtree Street
12th Floor, Suite 1200
Atlanta, GA 30309
Tel: +1-678-954-0670
Fax: +1-404-961-1892
Web:
http://www.evaristesys.com/